[PATCH] D52263: [InstCombine] Ignore vector compares in foldGEPIcmp()

[Jesper Antonsson via Phabricator via llvm-commits]

JesperAntonsson created this revision.
JesperAntonsson added reviewers: majnemer, spatel, lattner.

This is to fix PR38984 "InstCombine assertion at vector gep/icmp folding":
https://bugs.llvm.org/show_bug.cgi?id=38984

Vector icmps with this optimization opportunity seems exceedingly rare, so just avoid doing anything for this case.


Repository:
  rL LLVM

https://reviews.llvm.org/D52263

Files:
  lib/Transforms/InstCombine/InstCombineCompares.cpp
  test/Transforms/InstCombine/pr38984.ll


Index: test/Transforms/InstCombine/pr38984.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstCombine/pr38984.ll
@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -instcombine -S | FileCheck %s
+target datalayout = "p:16:16"
+
+ at offsets = external dso_local global [4 x i16], align 1
+
+define void @PR38984() {
+; CHECK-LABEL: @PR38984(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %0 = load i16, i16* getelementptr ([4 x i16], [4 x i16]* @offsets, i16 0, i16 undef), align 1
+  %1 = insertelement <4 x i16> undef, i16 %0, i32 3
+  %2 = sub <4 x i16> zeroinitializer, %1
+  %3 = sext <4 x i16> %2 to <4 x i32>
+  %4 = getelementptr inbounds i64, i64* null, <4 x i32> %3
+  %5 = ptrtoint <4 x i64*> %4 to <4 x i32>
+  %6 = getelementptr inbounds i64, i64* null, <4 x i16> %2
+  %7 = ptrtoint <4 x i64*> %6 to <4 x i32>
+  %8 = icmp eq <4 x i32> %5, %7
+  %9 = select <4 x i1> %8, <4 x i16> zeroinitializer, <4 x i16> <i16 1, i16 1, i16 1, i16 1>
+  %10 = sext <4 x i16> %9 to <4 x i32>
+  ret void
+}
Index: lib/Transforms/InstCombine/InstCombineCompares.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -974,10 +974,13 @@
           }
         }
 
-      if (NumDifferences == 0)   // SAME GEP?
-        return replaceInstUsesWith(I, // No comparison is needed here.
-                             Builder.getInt1(ICmpInst::isTrueWhenEqual(Cond)));
-
+      if (NumDifferences == 0) {  // SAME GEP?
+        Value *Replacement = Builder.getInt1(ICmpInst::isTrueWhenEqual(Cond));
+        // Ignore vector compares.
+        if (Replacement->getType() == I.getType())
+          return replaceInstUsesWith(I, // No comparison is needed here.
+                                     Replacement);
+      }
       else if (NumDifferences == 1 && GEPsInBounds) {
         Value *LHSV = GEPLHS->getOperand(DiffOperand);
         Value *RHSV = GEPRHS->getOperand(DiffOperand);


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