[DAG] Make strictfp attribute only restricts for libm and make non-math optimizations possible (#165464)

the patch 

[Add strictfp attribute to prevent unwanted optimizations of libm
calls](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.
For example, it prevent converting strlen and memcmp to milicode call
__strlen and __memcmp.

Author: diggerlin

llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -9456,7 +9456,9 @@ 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;
@@ -9476,7 +9478,9 @@ 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;
@@ -9509,11 +9513,10 @@ 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:

llvm/test/CodeGen/PowerPC/milicode32.ll

@@ -68,7 +68,41 @@ entry:
   ret i32 %call
 }
 
+define i32 @strlen_test_fp_strict(ptr noundef %str) nounwind {
+; CHECK-AIX-32-P9-LABEL: strlen_test_fp_strict:
+; CHECK-AIX-32-P9:       # %bb.0: # %entry
+; CHECK-AIX-32-P9-NEXT:    mflr r0
+; CHECK-AIX-32-P9-NEXT:    stwu r1, -64(r1)
+; CHECK-AIX-32-P9-NEXT:    stw r0, 72(r1)
+; CHECK-AIX-32-P9-NEXT:    stw r3, 60(r1)
+; CHECK-AIX-32-P9-NEXT:    bl .___strlen[PR]
+; CHECK-AIX-32-P9-NEXT:    nop
+; CHECK-AIX-32-P9-NEXT:    addi r1, r1, 64
+; CHECK-AIX-32-P9-NEXT:    lwz r0, 8(r1)
+; CHECK-AIX-32-P9-NEXT:    mtlr r0
+; CHECK-AIX-32-P9-NEXT:    blr
+;
+; CHECK-LINUX32-P9-LABEL: strlen_test_fp_strict:
+; CHECK-LINUX32-P9:       # %bb.0: # %entry
+; CHECK-LINUX32-P9-NEXT:    mflr r0
+; CHECK-LINUX32-P9-NEXT:    stwu r1, -16(r1)
+; CHECK-LINUX32-P9-NEXT:    stw r0, 20(r1)
+; CHECK-LINUX32-P9-NEXT:    stw r3, 12(r1)
+; CHECK-LINUX32-P9-NEXT:    bl strlen
+; CHECK-LINUX32-P9-NEXT:    lwz r0, 20(r1)
+; CHECK-LINUX32-P9-NEXT:    addi r1, r1, 16
+; CHECK-LINUX32-P9-NEXT:    mtlr r0
+; CHECK-LINUX32-P9-NEXT:    blr
+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) #0
+  ret i32 %call
+}
+
 declare i32 @strlen(ptr noundef) nounwind
+attributes #0 = { strictfp }
 
 define ptr @test_memmove(ptr noundef %destination, ptr noundef %source, i32 noundef %num) #0 {
 ; CHECK-AIX-32-P9-LABEL: test_memmove: