[NFC][InstCombine] Make check for sret in a vararg function clearer

We're trying to get the parameter index of sret and see if it's part of
a function's varargs.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D109335

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index a05fe7a..c3fc5ea 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2884,7 +2884,7 @@ bool InstCombinerImpl::transformConstExprCastCall(CallBase &Call) {
     // that are compatible with being a vararg call argument.
     unsigned SRetIdx;
     if (CallerPAL.hasAttrSomewhere(Attribute::StructRet, &SRetIdx) &&
-        SRetIdx > FT->getNumParams())
+        SRetIdx - AttributeList::FirstArgIndex >= FT->getNumParams())
       return false;
   }