[PATCH] D80975: [SCEV][IndVarSimplify] insert point should not be block front if the front instruction is a PHI

[ChenZheng via Phabricator via llvm-commits]

shchenz updated this revision to Diff 267792.
shchenz added a comment.

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Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D80975/new/

https://reviews.llvm.org/D80975

Files:
  llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
  llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
  llvm/test/Transforms/IndVarSimplify/widen-i32-i8ptr.ll


Index: llvm/test/Transforms/IndVarSimplify/widen-i32-i8ptr.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/IndVarSimplify/widen-i32-i8ptr.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -indvars -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-n32:64"
+
+define dso_local void @Widen_i32_i8ptr() local_unnamed_addr {
+; CHECK-LABEL: @Widen_i32_i8ptr(
+; CHECK: phi i8*
+; CHECK: phi i32
+entry:
+  %ptrids = alloca [15 x i8*], align 8
+  %arraydecay2032 = getelementptr inbounds [15 x i8*], [15 x i8*]* %ptrids, i64 0, i64 0
+  store i8** %arraydecay2032, i8*** inttoptr (i64 8 to i8***), align 8
+  br label %for.cond2106
+
+for.cond2106:                                     ; preds = %for.cond2106, %entry
+  %gid.0 = phi i8* [ null, %entry ], [ %incdec.ptr, %for.cond2106 ]
+  %i.0 = phi i32 [ 0, %entry ], [ %inc2117, %for.cond2106 ]
+  %incdec.ptr = getelementptr inbounds i8, i8* %gid.0, i64 1
+  %idxprom2114 = zext i32 %i.0 to i64
+  %arrayidx2115 = getelementptr inbounds [15 x i8*], [15 x i8*]* %ptrids, i64 0, i64 %idxprom2114
+  store i8* %gid.0, i8** %arrayidx2115, align 8
+  %inc2117 = add nuw nsw i32 %i.0, 1
+  br label %for.cond2106
+}
Index: llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
===================================================================
--- llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -53,7 +53,12 @@
   // Since we don't know the builder's insertion point is actually
   // where the uses will be added (only that it dominates it), we are
   // not allowed to move it.
-  BasicBlock::iterator BIP = Builder.GetInsertPoint();
+  Instruction *BIP = &*Builder.GetInsertPoint();
+
+  // IndVarSimplify sometimes sets the insertion point at the block start, even
+  // when there are PHIs at that point.  We must correct for this.
+  if (isa<PHINode>(*BIP))
+    BIP = &*BIP->getParent()->getFirstNonPHI();
 
   Instruction *Ret = nullptr;
 
@@ -65,7 +70,7 @@
           // If the cast isn't where we want it, create a new cast at IP.
           // Likewise, do not reuse a cast at BIP because it must dominate
           // instructions that might be inserted before BIP.
-          if (BasicBlock::iterator(CI) != IP || BIP == IP) {
+          if (BasicBlock::iterator(CI) != IP || BIP == &*IP) {
             // Create a new cast, and leave the old cast in place in case
             // it is being used as an insert point.
             Ret = CastInst::Create(Op, V, Ty, "", &*IP);
@@ -84,7 +89,7 @@
   // We assert at the end of the function since IP might point to an
   // instruction with different dominance properties than a cast
   // (an invoke for example) and not dominate BIP (but the cast does).
-  assert(SE.DT.dominates(Ret, &*BIP));
+  assert(SE.DT.dominates(Ret, BIP));
 
   rememberInstruction(Ret);
   return Ret;
Index: llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -1436,7 +1436,11 @@
   // expect a well-formed cyclic phi-with-increments. i.e. any operand not part
   // of the phi-SCC dominates the loop entry.
   Instruction *InsertPt = &L->getHeader()->front();
-  WidePhi = cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt));
+  WidePhi = dyn_cast<PHINode>(Rewriter.expandCodeFor(AddRec, WideType, InsertPt));
+  // If the wide phi is not a phi node, for example a cast node, like bitcast,
+  // inttoptr, ptrtoint, just skip for now.
+  if (!WidePhi)
+    return nullptr;
 
   // Remembering the WideIV increment generated by SCEVExpander allows
   // widenIVUse to reuse it when widening the narrow IV's increment. We don't


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