[PATCH] D24088: Create a getelementptr instead of sub expr for ValueOffsetPair if the value is a pointer

[Wei Mi via llvm-commits]

wmi updated this revision to Diff 70971.
wmi added a comment.

Address Sanjoy's comments. I wanted to find a testcase to test the case that the offset  is not divisible by the byte size of ETy but didn't succeed, so I forced the code to go through that branch and eyeball the output.


Repository:
  rL LLVM

https://reviews.llvm.org/D24088

Files:
  lib/Analysis/ScalarEvolutionExpander.cpp
  test/Analysis/ScalarEvolution/scev-expander-reuse-gep.ll

Index: test/Analysis/ScalarEvolution/scev-expander-reuse-gep.ll
===================================================================
--- test/Analysis/ScalarEvolution/scev-expander-reuse-gep.ll
+++ test/Analysis/ScalarEvolution/scev-expander-reuse-gep.ll
@@ -0,0 +1,36 @@
+; PR30213. Check scev expand will generate correct code if the value
+; in ValueOffsetPair is of pointer type.
+; RUN: opt < %s -loop-reduce -S | FileCheck %s
+
+; CHECK: %ptr4.ptr1 = select i1 %cmp.i, i8* %ptr4, i8* %ptr1
+; CHECK-NEXT: %scevgep = getelementptr i8, i8* %ptr4.ptr1, i32 1
+; CHECK-NEXT: br label %while.cond.i
+
+target datalayout = "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128"
+target triple = "i386-apple-macosx10.12.0"
+
+; Function Attrs: nounwind optsize ssp
+define void @Foo() {
+entry:
+  switch i2 undef, label %sw.epilog102 [
+    i2 -2, label %sw.bb28
+  ]
+
+sw.bb28:                                          ; preds = %entry
+  %0 = load i8*, i8** undef, align 2
+  %ptr1 = getelementptr inbounds i8, i8* undef, i32 -1
+  %ptr4 = getelementptr inbounds i8, i8* %0, i32 -1
+  %cmp.i = icmp ult i8* undef, %0
+  %ptr4.ptr1 = select i1 %cmp.i, i8* %ptr4, i8* %ptr1
+  br label %while.cond.i
+
+while.cond.i:                                     ; preds = %while.cond.i, %sw.bb28
+  %currPtr.1.i = phi i8* [ %incdec.ptr.i, %while.cond.i ], [ %ptr4.ptr1, %sw.bb28 ]
+  %incdec.ptr.i = getelementptr inbounds i8, i8* %currPtr.1.i, i32 1
+  %1 = load i8, i8* %incdec.ptr.i, align 1
+  br label %while.cond.i
+
+sw.epilog102:                                     ; preds = %entry
+  unreachable
+}
+
Index: lib/Analysis/ScalarEvolutionExpander.cpp
===================================================================
--- lib/Analysis/ScalarEvolutionExpander.cpp
+++ lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1703,9 +1703,29 @@
 
   if (!V)
     V = visit(S);
-  else if (VO.second)
-    V = Builder.CreateSub(V, VO.second);
-
+  else if (VO.second) {
+    if (V->getType()->isPointerTy()) {
+      PointerType *Vty = cast<PointerType>(V->getType());
+      Type *Ety = Vty->getPointerElementType();
+      int64_t Offset = VO.second->getSExtValue();
+      int64_t ESize = SE.getTypeSizeInBits(Ety);
+      if ((Offset * 8) % ESize == 0) {
+        ConstantInt *Idx = ConstantInt::getSigned(
+            VO.second->getType(), -Offset * 8 / SE.getTypeSizeInBits(Ety));
+        V = Builder.CreateGEP(Ety, V, Idx, "scevgep");
+      } else {
+        ConstantInt *Idx =
+            ConstantInt::getSigned(VO.second->getType(), -Offset);
+        unsigned AS = Vty->getAddressSpace();
+        V = Builder.CreateBitCast(V, Type::getInt8PtrTy(SE.getContext(), AS));
+        V = Builder.CreateGEP(Type::getInt8Ty(SE.getContext()), V, Idx,
+                              "scevgep");
+        V = Builder.CreateBitCast(V, Vty);
+      }
+    } else {
+      V = Builder.CreateSub(V, VO.second);
+    }
+  }
   // Remember the expanded value for this SCEV at this location.
   //
   // This is independent of PostIncLoops. The mapped value simply materializes


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