[InstSimplify] fold funnel shifts with undef operands

rotateright · rotateright · commit 14ab9170b802 · 2018-11-20T17:34:59.000Z
Splitting these off from the D54666.

Patch by: nikic (Nikita Popov)

llvm-svn: 347332
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5042,7 +5042,16 @@ static Value *simplifyIntrinsic(Function *F, IterTy ArgBegin, IterTy ArgEnd,
   }
   case Intrinsic::fshl:
   case Intrinsic::fshr: {
-    Value *ShAmtArg = ArgBegin[2];
+    Value *Op0 = ArgBegin[0], *Op1 = ArgBegin[1], *ShAmtArg = ArgBegin[2];
+
+    // If both operands are undef, the result is undef.
+    if (match(Op0, m_Undef()) && match(Op1, m_Undef()))
+      return UndefValue::get(F->getReturnType());
+
+    // If shift amount is undef, assume it is zero.
+    if (match(ShAmtArg, m_Undef()))
+      return ArgBegin[IID == Intrinsic::fshl ? 0 : 1];
+
     const APInt *ShAmtC;
     if (match(ShAmtArg, m_APInt(ShAmtC))) {
       // If there's effectively no shift, return the 1st arg or 2nd arg.
diff --git a/llvm/test/Transforms/InstSimplify/call.ll b/llvm/test/Transforms/InstSimplify/call.ll
@@ -632,17 +632,15 @@ define <2 x i8> @fshr_zero_shift_guard_splat(<2 x i8> %x, <2 x i8> %y, <2 x i8>
 
 define i8 @fshl_ops_undef(i8 %shamt) {
 ; CHECK-LABEL: @fshl_ops_undef(
-; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.fshl.i8(i8 undef, i8 undef, i8 [[SHAMT:%.*]])
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 undef
 ;
   %r = call i8 @llvm.fshl.i8(i8 undef, i8 undef, i8 %shamt)
   ret i8 %r
 }
 
 define i9 @fshr_ops_undef(i9 %shamt) {
 ; CHECK-LABEL: @fshr_ops_undef(
-; CHECK-NEXT:    [[R:%.*]] = call i9 @llvm.fshr.i9(i9 undef, i9 undef, i9 [[SHAMT:%.*]])
-; CHECK-NEXT:    ret i9 [[R]]
+; CHECK-NEXT:    ret i9 undef
 ;
   %r = call i9 @llvm.fshr.i9(i9 undef, i9 undef, i9 %shamt)
   ret i9 %r
@@ -652,17 +650,15 @@ define i9 @fshr_ops_undef(i9 %shamt) {
 
 define i8 @fshl_shift_undef(i8 %x, i8 %y) {
 ; CHECK-LABEL: @fshl_shift_undef(
-; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.fshl.i8(i8 [[X:%.*]], i8 [[Y:%.*]], i8 undef)
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 [[X:%.*]]
 ;
   %r = call i8 @llvm.fshl.i8(i8 %x, i8 %y, i8 undef)
   ret i8 %r
 }
 
 define i9 @fshr_shift_undef(i9 %x, i9 %y) {
 ; CHECK-LABEL: @fshr_shift_undef(
-; CHECK-NEXT:    [[R:%.*]] = call i9 @llvm.fshr.i9(i9 [[X:%.*]], i9 [[Y:%.*]], i9 undef)
-; CHECK-NEXT:    ret i9 [[R]]
+; CHECK-NEXT:    ret i9 [[Y:%.*]]
 ;
   %r = call i9 @llvm.fshr.i9(i9 %x, i9 %y, i9 undef)
   ret i9 %r
