Improve __builtin_constant_p lowering

[joerg]

Summary

__builtin_constant_p used to be short-cut evaluated to false when building with -O0. This is undesirable as it means that constant folding in the front-end can give different results than folding in the back-end. It can also create conditional branches on constant conditions that don't get folded away. With the improvements to the llvm.is.constant handling on the LLVM side, the short-cut is no longer useful.

Adjust various codegen tests to not depend on the optimizations.

[joerg]

Ping.

[rsmith]

OK, this is fine by me if you're confident this doesn't degrade the generated code at -O0.

clang/lib/CodeGen/CGBuiltin.cpp

RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
   case Builtin::BI_rotr16:
   case Builtin::BI_rotr:
   case Builtin::BI_lrotr:
   case Builtin::BI_rotr64:
     return emitRotate(E, true);
 
   case Builtin::BI__builtin_constant_p: {
     llvm::Type *ResultType = ConvertType(E->getType());
-    if (CGM.getCodeGenOpts().OptimizationLevel == 0)
-      // At -O0, we don't perform inlining, so we don't need to delay the
-      // processing.
-      return RValue::get(ConstantInt::get(ResultType, 0));
 
     const Expr *Arg = E->getArg(0);
     QualType ArgType = Arg->getType();
     // FIXME: The allowance for Obj-C pointers and block pointers is historical
     // and likely a mistake.
     if (!ArgType->isIntegralOrEnumerationType() && !ArgType->isFloatingType() &&
         !ArgType->isObjCObjectPointerType() && !ArgType->isBlockPointerType())
       // Per the GCC documentation, only numeric constants are recognized after

clang/test/CodeGen/builtin-constant-p.c

-// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s -O2 | FileCheck %s
-// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -o - %s -O0 | FileCheck --check-prefix=O0 %s
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -disable-llvm-optzns -o - %s -O2 | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -emit-llvm -disable-llvm-optzns -o - %s -O0 | FileCheck %s
 
 int a = 42;
 
-inline int bcp(int x) {
-  return __builtin_constant_p(x);
-}
-
 /* --- Compound literals */
 
 struct foo { int x, y; };
 
 int y;
 struct foo f = (struct foo){ __builtin_constant_p(y), 42 };
 
 struct foo test0(int expr) {
-  // CHECK: define i64 @test0(i32 %expr)
-  // CHECK: call i1 @llvm.is.constant.i32(i32 %expr)
+  // CHECK-LABEL: test0
+  // CHECK: call i1 @llvm.is.constant.i32
   struct foo f = (struct foo){ __builtin_constant_p(expr), 42 };
   return f;
 }
 
 /* --- Pointer types */
 
-inline int test1_i(int *x) {
-  return *x;
-}
-
 int test1() {
-  // CHECK: define i32 @test1
-  // CHECK: add nsw i32 %0, -13
-  // CHECK-NEXT: call i1 @llvm.is.constant.i32(i32 %sub)
-  return bcp(test1_i(&a) - 13);
-}
-
-int test2() {
-  // CHECK: define i32 @test2
+  // CHECK-LABEL: test1
   // CHECK: ret i32 0
   return __builtin_constant_p(&a - 13);
 }
 
-inline int test3_i(int *x) {
-  return 42;
-}
-
-int test3() {
-  // CHECK: define i32 @test3
-  // CHECK: ret i32 1
-  return bcp(test3_i(&a) - 13);
-}
-
 /* --- Aggregate types */
 
 int b[] = {1, 2, 3};
 
-int test4() {
-  // CHECK: define i32 @test4
+int test2() {
+  // CHECK-LABEL: test2
   // CHECK: ret i32 0
   return __builtin_constant_p(b);
 }
 
-const char test5_c[] = {1, 2, 3, 0};
+const char test3_c[] = {1, 2, 3, 0};
 
-int test5() {
-  // CHECK: define i32 @test5
+int test3() {
+  // CHECK-LABEL: test3
   // CHECK: ret i32 0
-  return __builtin_constant_p(test5_c);
+  return __builtin_constant_p(test3_c);
 }
 
-inline char test6_i(const char *x) {
+inline char test4_i(const char *x) {
   return x[1];
 }
 
-int test6() {
-  // CHECK: define i32 @test6
+int test4() {
+  // CHECK: define i32 @test4
   // CHECK: ret i32 0
-  return __builtin_constant_p(test6_i(test5_c));
-}
-
-/* --- Non-constant global variables */
-
-int test7() {
-  // CHECK: define i32 @test7
-  // CHECK: call i1 @llvm.is.constant.i32(i32 %0)
-  return bcp(a);
+  return __builtin_constant_p(test4_i(test3_c));
 }
 
 /* --- Constant global variables */
 
 const int c = 42;
 
-int test8() {
-  // CHECK: define i32 @test8
+int test5() {
+  // CHECK-LABEL: test5
   // CHECK: ret i32 1
-  return bcp(c);
+  return __builtin_constant_p(c);
 }
 
 /* --- Array types */
 
 int arr[] = { 1, 2, 3 };
 const int c_arr[] = { 1, 2, 3 };
 
-int test9() {
-  // CHECK: define i32 @test9
-  // CHECK: call i1 @llvm.is.constant.i32(i32 %0)
+int test6() {
+  // CHECK-LABEL: test6
+  // CHECK: call i1 @llvm.is.constant.i32
   return __builtin_constant_p(arr[2]);
 }
 
-int test10() {
-  // CHECK: define i32 @test10
-  // CHECK: ret i32 1
+int test7() {
+  // CHECK-LABEL: test7
+  // CHECK: call i1 @llvm.is.constant.i32
   return __builtin_constant_p(c_arr[2]);
 }
 
-int test11() {
-  // CHECK: define i32 @test11
+int test8() {
+  // CHECK-LABEL: test8
   // CHECK: ret i32 0
   return __builtin_constant_p(c_arr);
 }
 
 /* --- Function pointers */
 
-int test12() {
-  // CHECK: define i32 @test12
+int test9() {
+  // CHECK-LABEL: test9
   // CHECK: ret i32 0
-  return __builtin_constant_p(&test10);
+  return __builtin_constant_p(&test9);
 }
 
-int test13() {
-  // CHECK: define i32 @test13
+int test10() {
+  // CHECK-LABEL: test10
   // CHECK: ret i32 1
   return __builtin_constant_p(&test10 != 0);
 }
 
 typedef unsigned long uintptr_t;
 #define assign(p, v) ({ \
   uintptr_t _r_a_p__v = (uintptr_t)(v);                           \
   if (__builtin_constant_p(v) && _r_a_p__v == (uintptr_t)0) {     \

 })
 
 typedef void fn_p(void);
 extern fn_p *dest_p;
 
 static void src_fn(void) {
 }
 
-void test14() {
+void test11() {
   assign(dest_p, src_fn);
 }
 
-extern int test15_v;
+extern int test12_v;
 
-struct { const char *t; int a; } test15[] = {
-    { "tag", __builtin_constant_p(test15_v) && !test15_v ? 1 : 0 }
+struct { const char *t; int a; } test12[] = {
+    { "tag", __builtin_constant_p(test12_v) && !test12_v ? 1 : 0 }
 };
 
-extern char test16_v;
-struct { int a; } test16 = { __builtin_constant_p(test16_v) };
+extern char test13_v;
+struct { int a; } test13 = { __builtin_constant_p(test13_v) };
 
-extern unsigned long long test17_v;
+extern unsigned long long test14_v;
 
-void test17() {
-  // O0: define void @test17
-  // O0: call void asm sideeffect "", {{.*}}(i32 -1) 
-  // CHECK: define void @test17
+void test14() {
+  // CHECK-LABEL: test14
   // CHECK: call void asm sideeffect "", {{.*}}(i32 -1) 
-  __asm__ __volatile__("" :: "n"( (__builtin_constant_p(test17_v) || 0) ? 1 : -1));
+  __asm__ __volatile__("" :: "n"( (__builtin_constant_p(test14_v) || 0) ? 1 : -1));
 }
 
-int test18_f();
-// CHECK: define void @test18
-// CHECK-NOT: call {{.*}}test18_f
-void test18() {
+int test15_f();
+// CHECK-LABEL: define void @test15
+// CHECK-NOT: call {{.*}}test15_f
+void test15() {
   int a, b;
-  (void)__builtin_constant_p((a = b, test18_f()));
+  (void)__builtin_constant_p((a = b, test15_f()));
 }

clang/test/CodeGen/ppc-emmintrin.c

 // CHECK: store <2 x i64> [[REG141]], <2 x i64>* [[REG143:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: store i32 [[REG142]], i32* [[REG144:[0-9a-zA-Z_%.]+]], align 4
 // CHECK-NEXT: store <16 x i8> zeroinitializer, <16 x i8>* [[REG145:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: [[REG146:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG144]], align 4
 // CHECK-NEXT: [[REG147:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG146]], 16
 // CHECK-NEXT: br i1 [[REG147]], label %[[REG148:[0-9a-zA-Z_%.]+]], label %[[REG149:[0-9a-zA-Z_%.]+]]
 // CHECK: [[REG148]]:
 
-// CHECK-LE-NEXT: br i1 false, label %[[REG150:[0-9a-zA-Z_%.]+]], label %[[REG151:[0-9a-zA-Z_%.]+]]
+// CHECK-LE-NEXT: load
+// CHECK-LE-NEXT: call i1 @llvm.is.constant
+// CHECK-LE-NEXT: br i1 %[[REG1896a:[0-9a-zA-Z_%.]+]], label %[[REG150:[0-9a-zA-Z_%.]+]], label %[[REG151:[0-9a-zA-Z_%.]+]]
 // CHECK-LE: [[REG150]]:
 // CHECK-LE: [[REG152:[0-9a-zA-Z_%.]+]] = load <2 x i64>, <2 x i64>* [[REG143]], align 16
 // CHECK-LE-NEXT: [[REG153:[0-9a-zA-Z_%.]+]] = bitcast <2 x i64> [[REG152]] to <16 x i8>
 // CHECK-LE-NEXT: [[REG154:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG144]], align 4
 // CHECK-LE-NEXT: [[REG155:[0-9a-zA-Z_%.]+]] = sub nsw i32 16, [[REG154]]
 // CHECK-LE-NEXT: [[REG156:[0-9a-zA-Z_%.]+]] = call <16 x i8> @vec_sld(unsigned char vector[16], unsigned char vector[16], unsigned int)(<16 x i8> zeroinitializer, <16 x i8> [[REG153]], i32 zeroext [[REG155]])
 // CHECK-LE-NEXT: store <16 x i8> [[REG156]], <16 x i8>* [[REG157:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-LE-NEXT: br label %[[REG158:[0-9a-zA-Z_%.]+]]

 // CHECK-NEXT: br i1 [[REG1555]], label %[[REG1556:[0-9a-zA-Z_%.]+]], label %[[REG1557:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1556]]:
 // CHECK-NEXT: [[REG1558:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1552]], align 4
 // CHECK-NEXT: [[REG1559:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1558]], 16
 // CHECK-NEXT: br i1 [[REG1559]], label %[[REG1560:[0-9a-zA-Z_%.]+]], label %[[REG1557:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1560]]:
-// CHECK-NEXT: br i1 false, label %[[REG1561:[0-9a-zA-Z_%.]+]], label %[[REG1562:[0-9a-zA-Z_%.]+]]
+// CHECK-NEXT: load
+// CHECK-NEXT: call i1 @llvm.is.constant
+// CHECK-NEXT: br i1 %[[REG1561a:[0-9a-zA-Z_%.]+]], label %[[REG1561:[0-9a-zA-Z_%.]+]], label %[[REG1562:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1561]]:
 // CHECK-NEXT: [[REG1563:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1552]], align 4
 // CHECK-NEXT: [[REG1564:[0-9a-zA-Z_%.]+]] = trunc i32 [[REG1563]] to i8
 // CHECK-NEXT: [[REG1565:[0-9a-zA-Z_%.]+]] = call <8 x i16> @vec_splat_s16(signed char)(i8 signext [[REG1564]])
 // CHECK-NEXT: store <8 x i16> [[REG1565]], <8 x i16>* [[REG1566:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: br label %[[REG1567:[0-9a-zA-Z_%.]+]]
 

 // CHECK-NEXT: br i1 [[REG1583]], label %[[REG1584:[0-9a-zA-Z_%.]+]], label %[[REG1585:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1584]]:
 // CHECK-NEXT: [[REG1586:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1580]], align 4
 // CHECK-NEXT: [[REG1587:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1586]], 32
 // CHECK-NEXT: br i1 [[REG1587]], label %[[REG1588:[0-9a-zA-Z_%.]+]], label %[[REG1585:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1588]]:
-// CHECK-NEXT: br i1 false, label %[[REG1589:[0-9a-zA-Z_%.]+]], label %[[REG1590:[0-9a-zA-Z_%.]+]]
+// CHECK-NEXT: load
+// CHECK-NEXT: call i1 @llvm.is.constant
+// CHECK-NEXT: br i1 %{{[0-9a-zA-Z_%.]+}}, label %[[REG1589:[0-9a-zA-Z_%.]+]], label %[[REG1590:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1589]]:
 // CHECK-NEXT: [[REG1591:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1580]], align 4
 // CHECK-NEXT: [[REG1592:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1591]], 16
 // CHECK-NEXT: br i1 [[REG1592]], label %[[REG1593:[0-9a-zA-Z_%.]+]], label %[[REG1590:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1593]]:
 // CHECK-NEXT: [[REG1594:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1580]], align 4

 // CHECK-NEXT: br i1 [[REG1613]], label %[[REG1614:[0-9a-zA-Z_%.]+]], label %[[REG1615:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1614]]:
 // CHECK-NEXT: [[REG1616:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1610]], align 4
 // CHECK-NEXT: [[REG1617:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1616]], 64
 // CHECK-NEXT: br i1 [[REG1617]], label %[[REG1618:[0-9a-zA-Z_%.]+]], label %[[REG1615:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1618]]:
-// CHECK-NEXT: br i1 false, label %[[REG1619:[0-9a-zA-Z_%.]+]], label %[[REG1620:[0-9a-zA-Z_%.]+]]
+// CHECK-NEXT: load
+// CHECK-NEXT: call i1 @llvm.is.constant
+// CHECK-NEXT: br i1 %{{[0-9a-zA-Z_%.]+}}, label %[[REG1619:[0-9a-zA-Z_%.]+]], label %[[REG1620:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1619]]:
 // CHECK-NEXT: [[REG1621:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1610]], align 4
 // CHECK-NEXT: [[REG1622:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1621]], 16
 // CHECK-NEXT: br i1 [[REG1622]], label %[[REG1623:[0-9a-zA-Z_%.]+]], label %[[REG1620:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1623]]:
 // CHECK-NEXT: [[REG1624:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1610]], align 4

 // CHECK: store <2 x i64> [[REG1706]], <2 x i64>* [[REG1708:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: store i32 [[REG1707]], i32* [[REG1709:[0-9a-zA-Z_%.]+]], align 4
 // CHECK-NEXT: store <8 x i16> <i16 15, i16 15, i16 15, i16 15, i16 15, i16 15, i16 15, i16 15>, <8 x i16>* [[REG1710:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: [[REG1711:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1709]], align 4
 // CHECK-NEXT: [[REG1712:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1711]], 16
 // CHECK-NEXT: br i1 [[REG1712]], label %[[REG1713:[0-9a-zA-Z_%.]+]], label %[[REG1714:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1713]]:
-// CHECK-NEXT: br i1 false, label %[[REG1715:[0-9a-zA-Z_%.]+]], label %[[REG1716:[0-9a-zA-Z_%.]+]]
+// CHECK-NEXT: load
+// CHECK-NEXT: call i1 @llvm.is.constant
+// CHECK-NEXT: br i1 %[[REG1715a:[0-9a-zA-Z_%.]+]], label %[[REG1715:[0-9a-zA-Z_%.]+]], label %[[REG1716:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1715]]:
 // CHECK-NEXT: [[REG1717:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1709]], align 4
 // CHECK-NEXT: [[REG1718:[0-9a-zA-Z_%.]+]] = trunc i32 [[REG1717]] to i8
 // CHECK-NEXT: [[REG1719:[0-9a-zA-Z_%.]+]] = call <8 x i16> @vec_splat_s16(signed char)(i8 signext [[REG1718]])
 // CHECK-NEXT: store <8 x i16> [[REG1719]], <8 x i16>* [[REG1710]], align 16
 // CHECK-NEXT: br label %[[REG1720:[0-9a-zA-Z_%.]+]]
 

 // CHECK: store <2 x i64> [[REG1731]], <2 x i64>* [[REG1733:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: store i32 [[REG1732]], i32* [[REG1734:[0-9a-zA-Z_%.]+]], align 4
 // CHECK-NEXT: store <4 x i32> <i32 31, i32 31, i32 31, i32 31>, <4 x i32>* [[REG1735:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: [[REG1736:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1734]], align 4
 // CHECK-NEXT: [[REG1737:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1736]], 32
 // CHECK-NEXT: br i1 [[REG1737]], label %[[REG1738:[0-9a-zA-Z_%.]+]], label %[[REG1739:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1738]]:
-// CHECK-NEXT: br i1 false, label %[[REG1740:[0-9a-zA-Z_%.]+]], label %[[REG1741:[0-9a-zA-Z_%.]+]]
+// CHECK-NEXT: load
+// CHECK-NEXT: call i1 @llvm.is.constant
+// CHECK-NEXT: br i1 %[[REG1738:[0-9a-zA-Z_%.]+]], label %[[REG1740:[0-9a-zA-Z_%.]+]], label %[[REG1741:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1740]]:
 // CHECK-NEXT: [[REG1742:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1734]], align 4
 // CHECK-NEXT: [[REG1743:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1742]], 16
 // CHECK-NEXT: br i1 [[REG1743]], label %[[REG1744:[0-9a-zA-Z_%.]+]], label %[[REG1745:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1744]]:
 // CHECK-NEXT: [[REG1746:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1734]], align 4

 // CHECK: define available_externally <2 x i64> @_mm_srli_epi16(<2 x i64> [[REG1831:[0-9a-zA-Z_%.]+]], i32 signext [[REG1832:[0-9a-zA-Z_%.]+]])
 // CHECK: store <2 x i64> [[REG1831]], <2 x i64>* [[REG1833:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: store i32 [[REG1832]], i32* [[REG1834:[0-9a-zA-Z_%.]+]], align 4
 // CHECK-NEXT: store <8 x i16> zeroinitializer, <8 x i16>* [[REG1835:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: [[REG1836:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1834]], align 4
 // CHECK-NEXT: [[REG1837:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1836]], 16
 // CHECK-NEXT: br i1 [[REG1837]], label %[[REG1838:[0-9a-zA-Z_%.]+]], label %[[REG1839:[0-9a-zA-Z_%.]+]]
 // CHECK: [[REG1838]]:
-// CHECK-NEXT: br i1 false, label %[[REG1840:[0-9a-zA-Z_%.]+]], label %[[REG1841:[0-9a-zA-Z_%.]+]]
+// CHECK-NEXT: load
+// CHECK-NEXT: call i1 @llvm.is.constant
+// CHECK-NEXT: br i1 %[[REG1838a:[0-9a-zA-Z_%.]+]], label %[[REG1840:[0-9a-zA-Z_%.]+]], label %[[REG1841:[0-9a-zA-Z_%.]+]]
 // CHECK: [[REG1840]]:
 // CHECK-NEXT: [[REG1842:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1834]], align 4
 // CHECK-NEXT: [[REG1843:[0-9a-zA-Z_%.]+]] = trunc i32 [[REG1842]] to i8
 // CHECK-NEXT: [[REG1844:[0-9a-zA-Z_%.]+]] = call <8 x i16> @vec_splat_s16(signed char)(i8 signext [[REG1843]])
 // CHECK-NEXT: store <8 x i16> [[REG1844]], <8 x i16>* [[REG1845:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: br label %[[REG1846:[0-9a-zA-Z_%.]+]]
 // CHECK: [[REG1841]]:
 // CHECK-NEXT: [[REG1847:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1834]], align 4

 // CHECK: store <2 x i64> [[REG1856]], <2 x i64>* [[REG1858:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: store i32 [[REG1857]], i32* [[REG1859:[0-9a-zA-Z_%.]+]], align 4
 // CHECK-NEXT: store <4 x i32> zeroinitializer, <4 x i32>* [[REG1860:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: [[REG1861:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1859]], align 4
 // CHECK-NEXT: [[REG1862:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1861]], 32
 // CHECK-NEXT: br i1 [[REG1862]], label %[[REG1863:[0-9a-zA-Z_%.]+]], label %[[REG1864:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1863]]:
-// CHECK-NEXT: br i1 false, label %[[REG1865:[0-9a-zA-Z_%.]+]], label %[[REG1866:[0-9a-zA-Z_%.]+]]
+// CHECK-NEXT: load
+// CHECK-NEXT: call i1 @llvm.is.constant
+// CHECK-NEXT: br i1 %[[REG1865a:[0-9a-zA-Z_%.]+]], label %[[REG1865:[0-9a-zA-Z_%.]+]], label %[[REG1866:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1865]]:
 // CHECK-NEXT: [[REG1867:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1859]], align 4
 // CHECK-NEXT: [[REG1868:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1867]], 16
 // CHECK-NEXT: br i1 [[REG1868]], label %[[REG1869:[0-9a-zA-Z_%.]+]], label %[[REG1870:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1869]]:
 // CHECK-NEXT: [[REG1871:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1859]], align 4

 // CHECK: store <2 x i64> [[REG1887]], <2 x i64>* [[REG1889:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: store i32 [[REG1888]], i32* [[REG1890:[0-9a-zA-Z_%.]+]], align 4
 // CHECK-NEXT: store <2 x i64> zeroinitializer, <2 x i64>* [[REG1891:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: [[REG1892:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1890]], align 4
 // CHECK-NEXT: [[REG1893:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1892]], 64
 // CHECK-NEXT: br i1 [[REG1893]], label %[[REG1894:[0-9a-zA-Z_%.]+]], label %[[REG1895:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1894]]:
-// CHECK-NEXT: br i1 false, label %[[REG1896:[0-9a-zA-Z_%.]+]], label %[[REG1897:[0-9a-zA-Z_%.]+]]
+// CHECK-NEXT: load
+// CHECK-NEXT: call i1 @llvm.is.constant
+// CHECK-NEXT: br i1 %[[REG1896a:[0-9a-zA-Z_%.]+]], label %[[REG1896:[0-9a-zA-Z_%.]+]], label %[[REG1897:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1896]]:
 // CHECK-NEXT: [[REG1898:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1890]], align 4
 // CHECK-NEXT: [[REG1899:[0-9a-zA-Z_%.]+]] = icmp slt i32 [[REG1898]], 16
 // CHECK-NEXT: br i1 [[REG1899]], label %[[REG1900:[0-9a-zA-Z_%.]+]], label %[[REG1901:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG1900]]:
 // CHECK-NEXT: [[REG1902:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG1890]], align 4

clang/test/CodeGen/ppc-tmmintrin.c

 
 // CHECK-LABEL: @test_alignr
 
 // CHECK: define available_externally <2 x i64> @_mm_alignr_epi8(<2 x i64> [[REG61:[0-9a-zA-Z_%.]+]], <2 x i64> [[REG62:[0-9a-zA-Z_%.]+]], i32 zeroext [[REG63:[0-9a-zA-Z_%.]+]])
 // CHECK: [[REG64:[0-9a-zA-Z_%.]+]] = alloca i32, align 4
 // CHECK: store <2 x i64> [[REG61]], <2 x i64>* [[REG65:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: store <2 x i64> [[REG62]], <2 x i64>* [[REG66:[0-9a-zA-Z_%.]+]], align 16
 // CHECK-NEXT: store i32 [[REG63]], i32* [[REG64:[0-9a-zA-Z_%.]+]], align 4
-// CHECK-NEXT: br i1 false, label %[[REG67:[0-9a-zA-Z_%.]+]], label %[[REG68:[0-9a-zA-Z_%.]+]]
+// CHECK: %[[REG64b:[0-9a-zA-Z_%.]+]] = call i1 @llvm.is.constant.i32(i32 %0)
+// CHECK-NEXT: br i1 %[[REG64b]], label %[[REG67:[0-9a-zA-Z_%.]+]], label %[[REG68:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG67]]:
 // CHECK-NEXT: [[REG69:[0-9a-zA-Z_%.]+]] = load i32, i32* [[REG64]], align 4
 // CHECK-NEXT: [[REG70:[0-9a-zA-Z_%.]+]] = icmp ult i32 [[REG69]], 16
 // CHECK-NEXT: br i1 [[REG70]], label %[[REG71:[0-9a-zA-Z_%.]+]], label %[[REG68:[0-9a-zA-Z_%.]+]]
 
 // CHECK: [[REG71]]:
 // CHECK-BE-NEXT: load <2 x i64>, <2 x i64>* [[REG66]], align 16