Fix a bug in LoopStrengthReduce that caused it to emit IR with

use-before-def. The problem comes up in code with multiple PHIs where
one PHI is being rewritten in terms of the other, but the other needs
to be casted first. LLVM rules requre the cast instruction to be
inserted after any PHI instructions, but when instructions were
inserted to replace the second PHI value with a function of the first,
they were ended up going before the cast instruction. Avoid this
problem by remembering the location of the cast instruction, when one
is needed, and inserting the expansion of the new value after it.

This fixes a bug that surfaced in 255.vortex on x86-64 when
instcombine was removed from the middle of the loop optimization
passes. 

llvm-svn: 51169

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/X86/vortex-bug.ll b/llvm/test/CodeGen/X86/vortex-bug.ll
new file mode 100644
index 00000000000..680bfbdb349
--- /dev/null
+++ b/llvm/test/CodeGen/X86/vortex-bug.ll
@@ -0,0 +1,21 @@
+; RUN: llvm-as < %s | llc -march=x86
+
+	%struct.blktkntype = type { i32, i32 }
+	%struct.fieldstruc = type { [128 x i8], %struct.blktkntype*, i32, i32 }
+
+define fastcc i32 @Env_GetFieldStruc(i8* %FieldName, i32* %Status, %struct.fieldstruc* %FieldStruc) nounwind  {
+entry:
+	br label %bb137.i
+
+bb137.i:		; preds = %bb137.i, %entry
+	%FieldName_addr.0209.rec.i = phi i64 [ %tmp139.rec.i, %bb137.i ], [ 0, %entry ]		; <i64> [#uses=1]
+	%tmp147213.i = phi i32 [ %tmp147.i, %bb137.i ], [ 1, %entry ]		; <i32> [#uses=2]
+	%tmp139.rec.i = add i64 %FieldName_addr.0209.rec.i, 1		; <i64> [#uses=2]
+	%tmp141142.i = sext i32 %tmp147213.i to i64		; <i64> [#uses=0]
+	%tmp147.i = add i32 %tmp147213.i, 1		; <i32> [#uses=1]
+	br i1 false, label %bb137.i, label %bb149.i.loopexit
+
+bb149.i.loopexit:		; preds = %bb137.i
+	%tmp139.i = getelementptr i8* %FieldName, i64 %tmp139.rec.i		; <i8*> [#uses=0]
+	unreachable
+}