[PATCH] D78688: [ValueTracking] Handle shufflevector constants in ComputeNumSignBits

[Eli Friedman via Phabricator via llvm-commits]

efriedma created this revision.
efriedma added reviewers: spatel, huihuiz.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78688

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/nsw.ll


Index: llvm/test/Transforms/InstCombine/nsw.ll
===================================================================
--- llvm/test/Transforms/InstCombine/nsw.ll
+++ llvm/test/Transforms/InstCombine/nsw.ll
@@ -128,3 +128,15 @@
   ret <3 x i32> %t3
 }
 
+; Make sure we don't crash on a ConstantExpr shufflevector
+define <vscale x 2 x i64> @mul_nuw_nsw_shuffle_constant_expr(<vscale x 2 x i8> %z) {
+; CHECK-LABEL: @mul_nuw_nsw_shuffle_constant_expr(
+; CHECK-NEXT:    [[XX:%.*]] = zext <vscale x 2 x i8> [[Z:%.*]] to <vscale x 2 x i64>
+; CHECK-NEXT:    [[T3:%.*]] = mul <vscale x 2 x i64> [[XX]], shufflevector (<vscale x 2 x i64> insertelement (<vscale x 2 x i64> undef, i64 1, i32 0), <vscale x 2 x i64> zeroinitializer, <vscale x 2 x i32> zeroinitializer)
+; CHECK-NEXT:    ret <vscale x 2 x i64> [[T3]]
+;
+  %xx = zext <vscale x 2 x i8> %z to <vscale x 2 x i64>
+  %shuf = shufflevector <vscale x 2 x i64> insertelement (<vscale x 2 x i64> undef, i64 1, i32 0), <vscale x 2 x i64> zeroinitializer, <vscale x 2 x i32> zeroinitializer
+  %t3 = mul <vscale x 2 x i64> %shuf, %xx
+  ret <vscale x 2 x i64> %t3
+}
Index: llvm/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/lib/Analysis/ValueTracking.cpp
+++ llvm/lib/Analysis/ValueTracking.cpp
@@ -2907,7 +2907,11 @@
     case Instruction::ShuffleVector: {
       // Collect the minimum number of sign bits that are shared by every vector
       // element referenced by the shuffle.
-      auto *Shuf = cast<ShuffleVectorInst>(U);
+      auto *Shuf = dyn_cast<ShuffleVectorInst>(U);
+      if (!Shuf) {
+        // FIXME: Add support for shufflevector constant expressions.
+        return 1;
+      }
       APInt DemandedLHS, DemandedRHS;
       // For undef elements, we don't know anything about the common state of
       // the shuffle result.


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