From f20d70d57e1723d70b48b3f19868e17b9282bbfc Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 15 May 2008 23:26:57 +0000
Subject: [PATCH] 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.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51169 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopStrengthReduce.cpp | 24 +++++++++++++++++---
 test/CodeGen/X86/vortex-bug.ll               | 21 +++++++++++++++++
 2 files changed, 42 insertions(+), 3 deletions(-)
 create mode 100644 test/CodeGen/X86/vortex-bug.ll

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 6d66d14ec9a..dbd22d90e01 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -543,6 +543,7 @@ namespace {
     // operands of Inst to use the new expression 'NewBase', with 'Imm' added
     // to it.
     void RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
+                                        Instruction *InsertPt,
                                        SCEVExpander &Rewriter, Loop *L, Pass *P,
                                        SmallPtrSet<Instruction*,16> &DeadInsts);
     
@@ -603,8 +604,12 @@ Value *BasedUser::InsertCodeForBaseAtPosition(const SCEVHandle &NewBase,
 
 // Once we rewrite the code to insert the new IVs we want, update the
 // operands of Inst to use the new expression 'NewBase', with 'Imm' added
-// to it.
+// to it. NewBasePt is the last instruction which contributes to the
+// value of NewBase in the case that it's a diffferent instruction from
+// the PHI that NewBase is computed from, or null otherwise.
+//
 void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
+                                               Instruction *NewBasePt,
                                       SCEVExpander &Rewriter, Loop *L, Pass *P,
                                       SmallPtrSet<Instruction*,16> &DeadInsts) {
   if (!isa<PHINode>(Inst)) {
@@ -620,7 +625,10 @@ void BasedUser::RewriteInstructionToUseNewBase(const SCEVHandle &NewBase,
     // value will be pinned to live somewhere after the original computation.
     // In this case, we have to back off.
     if (!isUseOfPostIncrementedValue) {
-      if (Instruction *OpInst = dyn_cast<Instruction>(OperandValToReplace)) { 
+      if (NewBasePt) {
+        InsertPt = NewBasePt;
+        ++InsertPt;
+      } else if (Instruction *OpInst = dyn_cast<Instruction>(OperandValToReplace)) { 
         InsertPt = OpInst;
         while (isa<PHINode>(InsertPt)) ++InsertPt;
       }
@@ -1400,6 +1408,15 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
 
       SCEVHandle RewriteExpr = SE->getUnknown(RewriteOp);
 
+      // If we had to insert new instrutions for RewriteOp, we have to
+      // consider that they may not have been able to end up immediately
+      // next to RewriteOp, because non-PHI instructions may never precede
+      // PHI instructions in a block. In this case, remember where the last
+      // instruction was inserted so that we can use that point to expand
+      // the final RewriteExpr.
+      Instruction *NewBasePt = dyn_cast<Instruction>(RewriteOp);
+      if (RewriteOp == NewPHI) NewBasePt = 0;
+
       // Clear the SCEVExpander's expression map so that we are guaranteed
       // to have the code emitted where we expect it.
       Rewriter.clear();
@@ -1426,7 +1443,8 @@ void LoopStrengthReduce::StrengthReduceStridedIVUsers(const SCEVHandle &Stride,
         // Add BaseV to the PHI value if needed.
         RewriteExpr = SE->getAddExpr(RewriteExpr, SE->getUnknown(BaseV));
 
-      User.RewriteInstructionToUseNewBase(RewriteExpr, Rewriter, L, this,
+      User.RewriteInstructionToUseNewBase(RewriteExpr, NewBasePt,
+                                          Rewriter, L, this,
                                           DeadInsts);
 
       // Mark old value we replaced as possibly dead, so that it is elminated
diff --git a/test/CodeGen/X86/vortex-bug.ll b/test/CodeGen/X86/vortex-bug.ll
new file mode 100644
index 00000000000..680bfbdb349
--- /dev/null
+++ b/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
+}