[llvm] [WIP] Emit missed- and passed-optimization messages when partially inlining sqrt (PR #123966)

[via llvm-commits]

https://github.com/TiborGY updated https://github.com/llvm/llvm-project/pull/123966

>From 0831acdb9952ef8aed9d78e72aff34842241dcf2 Mon Sep 17 00:00:00 2001
From: GYT <tiborgyri at gmail.com>
Date: Wed, 22 Jan 2025 17:52:25 +0100
Subject: [PATCH] retry2

---
 .../Scalar/PartiallyInlineLibCalls.cpp        | 43 ++++++++++++++++---
 .../X86/good-prototype.ll                     |  3 +-
 2 files changed, 39 insertions(+), 7 deletions(-)

diff --git a/llvm/lib/Transforms/Scalar/PartiallyInlineLibCalls.cpp b/llvm/lib/Transforms/Scalar/PartiallyInlineLibCalls.cpp
index 2b50ccdc2eeb4f..898f1d096bb473 100644
--- a/llvm/lib/Transforms/Scalar/PartiallyInlineLibCalls.cpp
+++ b/llvm/lib/Transforms/Scalar/PartiallyInlineLibCalls.cpp
@@ -56,6 +56,20 @@ static bool optimizeSQRT(CallInst *Call, Function *CalledFunc,
   // dst = phi(v0, v1)
   //
 
+  ORE->emit([&]() {
+    return OptimizationRemark(DEBUG_TYPE, "SqrtPartiallyInlined",
+                              Call->getDebugLoc(), &CurrBB)
+           << "Partially inlined call to sqrt function despite having to use "
+              "errno for error handling: target has fast sqrt instruction";
+  });
+  ORE->emit([&]() {
+    return OptimizationRemarkMissed(DEBUG_TYPE, "BranchInserted",
+                                    Call->getDebugLoc(), &CurrBB)
+           << "Branch to library sqrt fn had to be inserted to satisfy the "
+              "current target's requirement for math functions to set errno on "
+              "invalid inputs";
+  });
+
   Type *Ty = Call->getType();
   IRBuilder<> Builder(Call->getNextNode());
 
@@ -125,18 +139,35 @@ static bool runPartiallyInlineLibCalls(Function &F, TargetLibraryInfo *TLI,
       if (!Call || !(CalledFunc = Call->getCalledFunction()))
         continue;
 
-      if (Call->isNoBuiltin() || Call->isStrictFP())
-        continue;
-
-      if (Call->isMustTailCall())
-        continue;
-
       // Skip if function either has local linkage or is not a known library
       // function.
       LibFunc LF;
       if (CalledFunc->hasLocalLinkage() ||
           !TLI->getLibFunc(*CalledFunc, LF) || !TLI->has(LF))
         continue;
+      if (Call->isNoBuiltin())
+        continue;
+      if (Call->isStrictFP()) {
+        ORE->emit([&]() {
+          OptimizationRemarkMissed(DEBUG_TYPE, "StrictFloat",
+                                   Call->getDebugLoc(), &CurrBB)
+          << "Could not consider library function for partial inlining:"
+             " strict FP exception behavior is active";
+        });
+        continue;
+      }
+      // Partially inlining a libcall that has the musttail attribute leads to
+      // broken LLVM IR, triggering an assertion in the IR verifier.
+      // Work around that by forgoing this optimization for musttail calls.
+      if (Call->isMustTailCall()) {
+        ORE->emit([&]() {
+          OptimizationRemarkMissed(DEBUG_TYPE, "MustTailCall",
+                                   Call->getDebugLoc(), &CurrBB)
+          << "Could not consider library function for partial inlining:"
+             " must tail call";
+        });
+        continue;
+      }
 
       switch (LF) {
       case LibFunc_sqrtf:
diff --git a/llvm/test/Transforms/PartiallyInlineLibCalls/X86/good-prototype.ll b/llvm/test/Transforms/PartiallyInlineLibCalls/X86/good-prototype.ll
index e6c2a7e629a5d6..afd4cde36ad09d 100644
--- a/llvm/test/Transforms/PartiallyInlineLibCalls/X86/good-prototype.ll
+++ b/llvm/test/Transforms/PartiallyInlineLibCalls/X86/good-prototype.ll
@@ -1,8 +1,9 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -S -passes=partially-inline-libcalls -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+; RUN: opt -S -passes=partially-inline-libcalls -mtriple=x86_64-unknown-linux-gnu -pass-remarks=partially-inline-libcalls < %s | FileCheck %s
 
 define float @f(float %val) {
 ; CHECK-LABEL: @f(
+; CHECK-REMARK: remark: partially-inline-libcalls: Partially inlined call to sqrt function despite having to use errno for error handling: target has fast sqrt instruction
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[RES:%.*]] = tail call float @sqrtf(float [[VAL:%.*]]) #[[READNONE:.*]]
 ; CHECK-NEXT:    [[TMP0:%.*]] = fcmp oge float [[VAL]], 0.000000e+00