[IPCP] Bail on extractvalue's with more than 1 index.

The replacement code only looks at the first index of the
extractvalue. If there are additional indices we'll end
up doing a bad replacement.

This only happens if the function returns a nested struct. Not
sure if clang ever generates such code. The original report came
from ispc.

Fixes PR43857

Differential Revision: https://reviews.llvm.org/D69656

Author: topperc

llvm/lib/Transforms/IPO/IPConstantPropagation.cpp

@@ -254,7 +254,7 @@ static bool PropagateConstantReturn(Function &F) {
       // Find the index of the retval to replace with
       int index = -1;
       if (ExtractValueInst *EV = dyn_cast<ExtractValueInst>(Ins))
-        if (EV->hasIndices())
+        if (EV->getNumIndices() == 1)
           index = *EV->idx_begin();
 
       // If this use uses a specific return value, and we have a replacement,

llvm/test/Transforms/IPConstantProp/PR43857.ll

@@ -0,0 +1,29 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -ipconstprop | FileCheck %s
+
+%struct.wobble = type { i32 }
+%struct.zot = type { %struct.wobble, %struct.wobble, %struct.wobble }
+
+declare dso_local fastcc float @bar(%struct.wobble* noalias, <8 x i32>) unnamed_addr
+
+define %struct.zot @widget(<8 x i32> %arg) local_unnamed_addr {
+; CHECK-LABEL: define {{[^@]+}}@widget(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    ret [[STRUCT_ZOT:%.*]] undef
+;
+bb:
+  ret %struct.zot undef
+}
+
+define void @baz(<8 x i32> %arg) local_unnamed_addr {
+; CHECK-LABEL: define {{[^@]+}}@baz(
+; CHECK-NEXT:  bb:
+; CHECK-NEXT:    [[TMP:%.*]] = call [[STRUCT_ZOT:%.*]] @widget(<8 x i32> [[ARG:%.*]])
+; CHECK-NEXT:    [[TMP1:%.*]] = extractvalue [[STRUCT_ZOT]] %tmp, 0, 0
+; CHECK-NEXT:    ret void
+;
+bb:
+  %tmp = call %struct.zot @widget(<8 x i32> %arg)
+  %tmp1 = extractvalue %struct.zot %tmp, 0, 0
+  ret void
+}