LoopIdiom: avoid patterned memset if constant is not relocatable.

[t.p.northover]

Summary

The pattern we're using for the memset_pattern* call gets put into a static global variable initialized, which means it has to be representable with relocations on the target. Most ConstantExpr instances do not satisfy this constraint, so avoid all of them for now.

[davide]

LGTM

[t.p.northover]

Thanks. Committed as 150595ab4be3.

llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp

 static Constant *getMemSetPatternValue(Value *V, const DataLayout *DL) {
   // FIXME: This could check for UndefValue because it can be merged into any
   // other valid pattern.
 
   // If the value isn't a constant, we can't promote it to being in a constant
   // array.  We could theoretically do a store to an alloca or something, but
   // that doesn't seem worthwhile.
   Constant *C = dyn_cast<Constant>(V);
-  if (!C)
+  if (!C || isa<ConstantExpr>(C))
     return nullptr;
 
   // Only handle simple values that are a power of two bytes in size.
   uint64_t Size = DL->getTypeSizeInBits(V->getType());
   if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
     return nullptr;
 
   // Don't care enough about darwin/ppc to implement this.

llvm/test/Transforms/LoopIdiom/basic.ll

for.body:                                         ; preds = %bb.nph, %for.body
   %indvar.next = add i64 %indvar, 1
   %exitcond = icmp eq i64 %indvar.next, %Size
   br i1 %exitcond, label %for.end, label %for.body
 
 for.end:                                          ; preds = %for.body, %entry
   ret void
 }
 
+%class.CMSPULog = type { %struct._opaque_pthread_mutex_t, ptr, i32, i32, i32, i8, i8, i8, [512 x i32] }
+%struct._opaque_pthread_mutex_t = type { i64, [56 x i8] }
+
+define noalias ptr @_ZN8CMSPULog9beginImplEja(ptr nocapture writeonly %0) local_unnamed_addr #0 {
+; CHECK-LABEL: @_ZN8CMSPULog9beginImplEja(
+; CHECK-NEXT:    br label [[TMP2:%.*]]
+; CHECK:       2:
+; CHECK-NEXT:    [[TMP3:%.*]] = phi i32 [ 0, [[TMP1:%.*]] ], [ [[TMP4:%.*]], [[TMP2]] ]
+; CHECK-NEXT:    [[TMP4]] = add nuw nsw i32 [[TMP3]], 1
+; CHECK-NEXT:    [[TMP5:%.*]] = zext i32 [[TMP3]] to i64
+; CHECK-NEXT:    [[TMP6:%.*]] = getelementptr [[CLASS_CMSPULOG:%.*]], ptr [[TMP0:%.*]], i64 0, i32 8, i64 [[TMP5]]
+; CHECK-NEXT:    store i32 trunc (i64 and (i64 ptrtoint (ptr @G to i64), i64 16777215) to i32), ptr [[TMP6]], align 4
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp ult i32 [[TMP3]], 511
+; CHECK-NEXT:    br i1 [[TMP7]], label [[TMP2]], label [[TMP8:%.*]]
+; CHECK:       8:
+; CHECK-NEXT:    ret ptr null
+;
+  br label %2
+
+2:                                                ; preds = %1, %2
+  %3 = phi i32 [ 0, %1 ], [ %4, %2 ]
+  %4 = add nuw nsw i32 %3, 1
+  %5 = zext i32 %3 to i64
+  %6 = getelementptr %class.CMSPULog, ptr %0, i64 0, i32 8, i64 %5
+  store i32 trunc (i64 and (i64 ptrtoint (ptr @G to i64), i64 16777215) to i32), ptr %6, align 4
+  %7 = icmp ult i32 %3, 511
+  br i1 %7, label %2, label %8
+
+8:                                                ; preds = %2
+  ret ptr null
+}
+
 ; Validate that "memset_pattern" has the proper attributes.