[InstCombine] Teach SimplifyDemandedVectorElts how to handle ConstantVector select...

If the mask of a select instruction is a ConstantVector, method
SimplifyDemandedVectorElts iterates over the mask elements to identify which
values are selected from the select inputs.

Before this patch, method SimplifyDemandedVectorElts always used method
Constant::isNullValue() to check if a value in the mask was zero. Unfortunately
that method always returns false when called on a ConstantExpr.

This patch fixes the problem in SimplifyDemandedVectorElts by adding an explicit
check for ConstantExpr values. Now, if a value in the mask is a ConstantExpr, we
avoid calling isNullValue() on it.

Fixes PR24922.

Differential Revision: http://reviews.llvm.org/D13219

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249390 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index a1fbda7f7e6d344324b1b4570740300acbd85814..743d51483ea16048fbeb0621a71b49b2b7e54ff8 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1057,7 +1057,13 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
     APInt LeftDemanded(DemandedElts), RightDemanded(DemandedElts);
     if (ConstantVector* CV = dyn_cast<ConstantVector>(I->getOperand(0))) {
       for (unsigned i = 0; i < VWidth; i++) {
-        if (CV->getAggregateElement(i)->isNullValue())
+        Constant *CElt = CV->getAggregateElement(i);
+        // Method isNullValue always returns false when called on a
+        // ConstantExpr. If CElt is a ConstantExpr then skip it in order to
+        // to avoid propagating incorrect information.
+        if (isa<ConstantExpr>(CElt))
+          continue;
+        if (CElt->isNullValue())
           LeftDemanded.clearBit(i);
         else
           RightDemanded.clearBit(i);

diff --git a/test/Transforms/InstCombine/vec_demanded_elts.ll b/test/Transforms/InstCombine/vec_demanded_elts.ll
index 5a2825ebfc3f3e6e2cf9748ca05a59abf233ad74..0b9663300c39a46760fab79b29b2d53a7f83d59a 100644 (file)
--- a/test/Transforms/InstCombine/vec_demanded_elts.ll
+++ b/test/Transforms/InstCombine/vec_demanded_elts.ll
@@ -253,3 +253,16 @@ define <4 x double> @test_vpermilvar_pd_256_zero(<4 x double> %v) {
   %a = tail call <4 x double> @llvm.x86.avx.vpermilvar.pd.256(<4 x double> %v, <4 x i64> zeroinitializer)
   ret <4 x double> %a
 }
+
+define <2 x i64> @PR24922(<2 x i64> %v) {
+; CHECK-LABEL: @PR24922
+; CHECK: select <2 x i1> 
+;
+; Check that instcombine doesn't wrongly fold the select statement into a
+; ret <2 x i64> %v
+;
+; FIXME: We should be able to simplify the ConstantExpr in the select mask.
+entry:
+  %result = select <2 x i1> <i1 icmp eq (i64 extractelement (<2 x i64> bitcast (<4 x i32> <i32 15, i32 15, i32 15, i32 15> to <2 x i64>), i64 0), i64 0), i1 true>, <2 x i64> %v, <2 x i64> zeroinitializer
+  ret <2 x i64> %result
+}