[llvm] [GlobalOpt] Don't query TTI on a llvm.memcpy declaration. (PR #127760)

[Craig Topper via llvm-commits]

https://github.com/topperc created https://github.com/llvm/llvm-project/pull/127760

Querying TTI creates a Subtarget object, but an llvm.memcpy declaration doesn't have target-cpu and target-feature attributes like functions with definitions. This can cause a warning to be printed on RISC-V because the target-abi in the Module requires floating point, but the subtarget features don't enable floating point. So far we've only seen this in LTO when an -mcpu is not supplied for the TargetMachine.

To fix this, get TTI for the calling function instead.

Fixes the issue reported here https://github.com/llvm/llvm-project/issues/69780#issuecomment-2665273161

>From ac5868bfd1e2cc31fc7bf4fdccd14bf8777e169b Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper at sifive.com>
Date: Tue, 18 Feb 2025 23:50:55 -0800
Subject: [PATCH] [GlobalOpt] Don't query TTI on a llvm.memcpy declaration.

Querying TTI creates a Subtarget object, but an llvm.memcpy
declaration doesn't have target-cpu and target-feature attributes
like functions with definitions. This can cause a warning to be printed
on RISC-V because the target-abi in the Module requires floating
point, but the subtarget features don't enable floating point.
So far we've only seen this in LTO when an -mcpu is not supplied
for the TargetMachine.

To fix this, get TTI for the calling function instead.
---
 llvm/lib/Transforms/IPO/GlobalOpt.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Transforms/IPO/GlobalOpt.cpp b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
index 9586fc97a39f7..1a2a27d22ae68 100644
--- a/llvm/lib/Transforms/IPO/GlobalOpt.cpp
+++ b/llvm/lib/Transforms/IPO/GlobalOpt.cpp
@@ -2186,8 +2186,10 @@ static bool tryWidenGlobalArraysUsedByMemcpy(
     if (NumElementsToCopy != DZSize || DZSize != SZSize)
       continue;
 
-    unsigned NumBytesToPad = GetTTI(*F).getNumBytesToPadGlobalArray(
-        NumBytesToCopy, SourceDataArray->getType());
+    unsigned NumBytesToPad =
+        GetTTI(*CI->getFunction())
+            .getNumBytesToPadGlobalArray(NumBytesToCopy,
+                                         SourceDataArray->getType());
     if (NumBytesToPad) {
       return tryWidenGlobalArrayAndDests(F, GV, NumBytesToPad, NumBytesToCopy,
                                          BytesToCopyOp, SourceDataArray);