[llvm] [LLC] Let strictfp attribute only work for libm (PR #165464)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-powerpc

Author: zhijian lin (diggerlin)

<details>
<summary>Changes</summary>

the patch 
```
commit 53a5fbb45fa45cba48963a6b17defa4c4f072d9d
Author: Andrew Kaylor <andrew.kaylor@<!-- -->intel.com>
Date:   Mon Aug 14 21:15:13 2017 +0000

    Add strictfp attribute to prevent unwanted optimizations of libm calls

    Differential Revision: https://reviews.llvm.org/D34163
```
  
  add `I.isStrictFP()` into 
```
  if (!I.isNoBuiltin() && !I.isStrictFP() && !F->hasLocalLinkage() &&
        F->hasName() && LibInfo->getLibFunc(*F, Func) &&
        LibInfo->hasOptimizedCodeGen(Func)) 
```

 it prevents the backend from optimizing even non-math libcalls such as `strlen` and `memcmp` if a call has the strict floating-point attribute.

---
Full diff: https://github.com/llvm/llvm-project/pull/165464.diff


2 Files Affected:

- (modified) llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp (+9-6) 
- (modified) llvm/test/CodeGen/PowerPC/milicode32.ll (+2-1) 


``````````diff
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index a52265055c88a..37108aa3a56d8 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -9392,7 +9392,9 @@ bool SelectionDAGBuilder::visitStrNLenCall(const CallInst &I) {
 bool SelectionDAGBuilder::visitUnaryFloatCall(const CallInst &I,
                                               unsigned Opcode) {
   // We already checked this call's prototype; verify it doesn't modify errno.
-  if (!I.onlyReadsMemory())
+  // Do not perform optimizations for call sites that require strict
+  // floating-point semantics.
+  if (!I.onlyReadsMemory() || I.isStrictFP())
     return false;
 
   SDNodeFlags Flags;
@@ -9412,7 +9414,9 @@ bool SelectionDAGBuilder::visitUnaryFloatCall(const CallInst &I,
 bool SelectionDAGBuilder::visitBinaryFloatCall(const CallInst &I,
                                                unsigned Opcode) {
   // We already checked this call's prototype; verify it doesn't modify errno.
-  if (!I.onlyReadsMemory())
+  // Do not perform optimizations for call sites that require strict
+  // floating-point semantics.
+  if (!I.onlyReadsMemory() || I.isStrictFP())
     return false;
 
   SDNodeFlags Flags;
@@ -9445,11 +9449,10 @@ void SelectionDAGBuilder::visitCall(const CallInst &I) {
 
     // Check for well-known libc/libm calls.  If the function is internal, it
     // can't be a library call.  Don't do the check if marked as nobuiltin for
-    // some reason or the call site requires strict floating point semantics.
+    // some reason.
     LibFunc Func;
-    if (!I.isNoBuiltin() && !I.isStrictFP() && !F->hasLocalLinkage() &&
-        F->hasName() && LibInfo->getLibFunc(*F, Func) &&
-        LibInfo->hasOptimizedCodeGen(Func)) {
+    if (!I.isNoBuiltin() && !F->hasLocalLinkage() && F->hasName() &&
+        LibInfo->getLibFunc(*F, Func) && LibInfo->hasOptimizedCodeGen(Func)) {
       switch (Func) {
       default: break;
       case LibFunc_bcmp:
diff --git a/llvm/test/CodeGen/PowerPC/milicode32.ll b/llvm/test/CodeGen/PowerPC/milicode32.ll
index 78d036202fe4e..09239fb9d1b09 100644
--- a/llvm/test/CodeGen/PowerPC/milicode32.ll
+++ b/llvm/test/CodeGen/PowerPC/milicode32.ll
@@ -64,8 +64,9 @@ entry:
   %str.addr = alloca ptr, align 4
   store ptr %str, ptr %str.addr, align 4
   %0 = load ptr, ptr %str.addr, align 4
-  %call = call i32 @strlen(ptr noundef %0)
+  %call = call i32 @strlen(ptr noundef %0) #0
   ret i32 %call
 }
 
 declare i32 @strlen(ptr noundef) nounwind
+attributes #0 = { strictfp }

``````````

</details>


https://github.com/llvm/llvm-project/pull/165464