[X86] Limit store merge size when implicitfloat is enabled (PR34421)

[RKSimon]

Summary

As suggested by @niravd : https://bugs.llvm.org/show_bug.cgi?id=34421#c2

[niravd]

The attributes in the test case can probably be pruned, but otherwise LGTM. Thanks.

[RKSimon]

In D37464#860982, @niravd wrote:

The attributes in the test case can probably be pruned, but otherwise LGTM. Thanks.

Thanks, I've stripped the attributes down in the commit.

lib/Target/X86/X86ISelLowering.h

public:
     EmitInstrWithCustomInserter(MachineInstr &MI,
                                 MachineBasicBlock *MBB) const override;
 
     /// This method returns the name of a target specific DAG node.
     const char *getTargetNodeName(unsigned Opcode) const override;
 
     bool mergeStoresAfterLegalization() const override { return true; }
 
+    bool canMergeStoresTo(unsigned AddressSpace, EVT MemVT,
+                          const SelectionDAG &DAG) const override;
+
     bool isCheapToSpeculateCttz() const override;
 
     bool isCheapToSpeculateCtlz() const override;
 
     bool isCtlzFast() const override;
 
     bool hasBitPreservingFPLogic(EVT VT) const override {
       return VT == MVT::f32 || VT == MVT::f64 || VT.isVector();

lib/Target/X86/X86ISelLowering.cpp

bool X86TargetLowering::isCheapToSpeculateCttz() const {
   return Subtarget.hasBMI();
 }
 
 bool X86TargetLowering::isCheapToSpeculateCtlz() const {
   // Speculate ctlz only if we can directly use LZCNT.
   return Subtarget.hasLZCNT();
 }
 
+bool X86TargetLowering::canMergeStoresTo(unsigned AddressSpace, EVT MemVT,
+                                         const SelectionDAG &DAG) const {
+  // Do not merge to float value size (128 bytes) if no implicit
+  // float attribute is set.
+  bool NoFloat = DAG.getMachineFunction().getFunction()->hasFnAttribute(
+      Attribute::NoImplicitFloat);
+
+  if (NoFloat) {
+    unsigned MaxIntSize = Subtarget.is64Bit() ? 64 : 32;
+    return (MemVT.getSizeInBits() <= MaxIntSize);
+  }
+  return true;
+}
+
 bool X86TargetLowering::isCtlzFast() const {
   return Subtarget.hasFastLZCNT();
 }
 
 bool X86TargetLowering::isMaskAndCmp0FoldingBeneficial(
     const Instruction &AndI) const {
   return true;
 }

test/CodeGen/X86/pr34421.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=i686-apple-macosx10.13.0 | FileCheck %s --check-prefix=X86
+; RUN: llc < %s -mtriple=x86_64-apple-macosx10.13.0 | FileCheck %s --check-prefix=X64
+
+; Function Attrs: noimplicitfloat noredzone nounwind
+define void @thread_selfcounts() local_unnamed_addr #0 {
+; X86-LABEL: thread_selfcounts:
+; X86:       ## BB#0: ## %entry
+; X86-NEXT:    pushl %ebp
+; X86-NEXT:    movl %esp, %ebp
+; X86-NEXT:    subl $56, %esp
+; X86-NEXT:    movl -56(%ebp), %eax
+; X86-NEXT:    movl -52(%ebp), %ecx
+; X86-NEXT:    movl %ecx, -20(%ebp)
+; X86-NEXT:    movl %eax, -24(%ebp)
+; X86-NEXT:    movl -48(%ebp), %eax
+; X86-NEXT:    movl -44(%ebp), %ecx
+; X86-NEXT:    movl %ecx, -12(%ebp)
+; X86-NEXT:    movl %eax, -16(%ebp)
+; X86-NEXT:    ## -- End function
+;
+; X64-LABEL: thread_selfcounts:
+; X64:       ## BB#0: ## %entry
+; X64-NEXT:    pushq %rbp
+; X64-NEXT:    movq %rsp, %rbp
+; X64-NEXT:    subq $48, %rsp
+; X64-NEXT:    movq -48(%rbp), %rax
+; X64-NEXT:    movq -40(%rbp), %rcx
+; X64-NEXT:    movq %rax, -16(%rbp)
+; X64-NEXT:    movq %rcx, -8(%rbp)
+; X64-NEXT:    ## -- End function
+entry:
+  %counts = alloca [2 x i64], align 16
+  %thread_counts = alloca [3 x i64], align 16
+  %arraydecay = getelementptr inbounds [3 x i64], [3 x i64]* %thread_counts, i64 0, i64 0
+  %0 = load i64, i64* %arraydecay, align 16
+  %arrayidx3 = getelementptr inbounds [2 x i64], [2 x i64]* %counts, i64 0, i64 0
+  store i64 %0, i64* %arrayidx3, align 16
+  %arrayidx6 = getelementptr inbounds [3 x i64], [3 x i64]* %thread_counts, i64 0, i64 1
+  %1 = load i64, i64* %arrayidx6, align 8
+  %arrayidx10 = getelementptr inbounds [2 x i64], [2 x i64]* %counts, i64 0, i64 1
+  store i64 %1, i64* %arrayidx10, align 8
+  unreachable
+}
+
+attributes #0 = { noimplicitfloat noredzone nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="penryn" "target-features"="+cx16,+fxsr,+mmx,+sse,+sse2,+sse3,+sse4.1,+ssse3,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }