llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT--> @llvm/pr-subscribers-backend-x86 Author: Feng Zou (fzou1) <details> <summary>Changes</summary> For more details about this feature, please refer to latest Intel 64 and IA-32 Architectures Optimization Reference Manual Volume 1: https://www.intel.com/content/www/us/en/content-details/821612/intel-64-and-ia-32-architectures-optimization-reference-manual-volume-1.html --- Full diff: https://github.com/llvm/llvm-project/pull/97721.diff 5 Files Affected: - (modified) clang/lib/Basic/Targets/X86.cpp (+3) - (modified) clang/lib/Basic/Targets/X86.h (+1) - (modified) llvm/lib/Target/X86/X86.td (+10-3) - (modified) llvm/lib/Target/X86/X86MCInstLower.cpp (+24) - (added) llvm/test/CodeGen/X86/branch-hint.ll (+95) ``````````diff diff --git a/clang/lib/Basic/Targets/X86.cpp b/clang/lib/Basic/Targets/X86.cpp index 276d492955207..1f6fc842ddd95 100644 --- a/clang/lib/Basic/Targets/X86.cpp +++ b/clang/lib/Basic/Targets/X86.cpp @@ -457,6 +457,8 @@ bool X86TargetInfo::handleTargetFeatures(std::vector<std::string> &Features, HasCF = true; } else if (Feature == "+zu") { HasZU = true; + } else if (Feature == "+branch-hint") { + HasBranchHint = true; } X86SSEEnum Level = llvm::StringSwitch<X86SSEEnum>(Feature) @@ -1292,6 +1294,7 @@ bool X86TargetInfo::hasFeature(StringRef Feature) const { .Case("nf", HasNF) .Case("cf", HasCF) .Case("zu", HasZU) + .Case("branch-hint", HasBranchHint) .Default(false); } diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h index 5ce4953251bc3..a70711f4ae2bb 100644 --- a/clang/lib/Basic/Targets/X86.h +++ b/clang/lib/Basic/Targets/X86.h @@ -174,6 +174,7 @@ class LLVM_LIBRARY_VISIBILITY X86TargetInfo : public TargetInfo { bool HasCF = false; bool HasZU = false; bool HasInlineAsmUseGPR32 = false; + bool HasBranchHint = false; protected: llvm::X86::CPUKind CPU = llvm::X86::CK_None; diff --git a/llvm/lib/Target/X86/X86.td b/llvm/lib/Target/X86/X86.td index 68b78c7c44771..fdd7d5f1ee0e7 100644 --- a/llvm/lib/Target/X86/X86.td +++ b/llvm/lib/Target/X86/X86.td @@ -749,6 +749,11 @@ def TuningUseGLMDivSqrtCosts : SubtargetFeature<"use-glm-div-sqrt-costs", "UseGLMDivSqrtCosts", "true", "Use Goldmont specific floating point div/sqrt costs">; +// Starting with Redwood Cove architecture, the branch has branch taken hint +// (i.e., instruction prefix 3EH). +def TuningBranchHint: SubtargetFeature<"branch-hint", "HasBranchHint", "true", + "Target has branch hint feature">; + //===----------------------------------------------------------------------===// // X86 CPU Families // TODO: Remove these - use general tuning features to determine codegen. @@ -1124,6 +1129,8 @@ def ProcessorFeatures { FeaturePREFETCHI]; list<SubtargetFeature> GNRFeatures = !listconcat(SPRFeatures, GNRAdditionalFeatures); + list<SubtargetFeature> GNRAdditionalTuning = [TuningBranchHint]; + list<SubtargetFeature> GNRTuning = !listconcat(SPRTuning, GNRAdditionalTuning); // Graniterapids D list<SubtargetFeature> GNRDAdditionalFeatures = [FeatureAMXCOMPLEX]; @@ -1815,12 +1822,12 @@ def : ProcModel<"pantherlake", AlderlakePModel, def : ProcModel<"clearwaterforest", AlderlakePModel, ProcessorFeatures.CWFFeatures, ProcessorFeatures.ADLTuning>; def : ProcModel<"graniterapids", SapphireRapidsModel, - ProcessorFeatures.GNRFeatures, ProcessorFeatures.SPRTuning>; + ProcessorFeatures.GNRFeatures, ProcessorFeatures.GNRTuning>; def : ProcModel<"emeraldrapids", SapphireRapidsModel, - ProcessorFeatures.SPRFeatures, ProcessorFeatures.SPRTuning>; + ProcessorFeatures.SPRFeatures, ProcessorFeatures.GNRTuning>; foreach P = ["graniterapids-d", "graniterapids_d"] in { def : ProcModel<P, SapphireRapidsModel, - ProcessorFeatures.GNRDFeatures, ProcessorFeatures.SPRTuning>; + ProcessorFeatures.GNRDFeatures, ProcessorFeatures.GNRTuning>; } // AMD CPUs. diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp index 00f58f9432e4d..34d95573585c9 100644 --- a/llvm/lib/Target/X86/X86MCInstLower.cpp +++ b/llvm/lib/Target/X86/X86MCInstLower.cpp @@ -25,6 +25,7 @@ #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallString.h" #include "llvm/ADT/StringExtras.h" +#include "llvm/CodeGen/MachineBranchProbabilityInfo.h" #include "llvm/CodeGen/MachineConstantPool.h" #include "llvm/CodeGen/MachineFunction.h" #include "llvm/CodeGen/MachineModuleInfoImpls.h" @@ -54,6 +55,14 @@ using namespace llvm; +static cl::opt<bool> EnableBranchHint("branch-hint", + cl::desc("Enable branch hint."), + cl::init(false), cl::Hidden); +static cl::opt<unsigned> BranchHintProbabilityThreshold( + "branch-hint-probability-threshold", + cl::desc("The probability threshold of enabling branch hint."), + cl::init(50), cl::Hidden); + namespace { /// X86MCInstLower - This class is used to lower an MachineInstr into an MCInst. @@ -2444,6 +2453,21 @@ void X86AsmPrinter::emitInstruction(const MachineInstr *MI) { if (IndCSPrefix && MI->hasRegisterImplicitUseOperand(X86::R11)) EmitAndCountInstruction(MCInstBuilder(X86::CS_PREFIX)); break; + case X86::JCC_1: + // Two instruction prefixes (2EH for branch not-taken and 3EH for branch + // taken) are used as branch hints. Here we add branch taken prefix for + // jump instruction with higher probability than threshold. + if (getSubtarget().hasBranchHint() && EnableBranchHint) { + const MachineBranchProbabilityInfo *MBPI = + &getAnalysis<MachineBranchProbabilityInfoWrapperPass>().getMBPI(); + MachineBasicBlock *DestBB = MI->getOperand(0).getMBB(); + BranchProbability EdgeProb = + MBPI->getEdgeProbability(MI->getParent(), DestBB); + BranchProbability Threshold(BranchHintProbabilityThreshold, 100); + if (EdgeProb > Threshold) + EmitAndCountInstruction(MCInstBuilder(X86::DS_PREFIX)); + } + break; } MCInst TmpInst; diff --git a/llvm/test/CodeGen/X86/branch-hint.ll b/llvm/test/CodeGen/X86/branch-hint.ll new file mode 100644 index 0000000000000..7bef84c34d10f --- /dev/null +++ b/llvm/test/CodeGen/X86/branch-hint.ll @@ -0,0 +1,95 @@ +; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py +; RUN: llc < %s -mtriple=x86_64-linux -branch-hint -branch-hint-probability-threshold=60 -show-mc-encoding | FileCheck %s + +; Design: Insert "ds # encoding: [0x3e]" for condition branches who has high probability to take. +; Source code: +; int XX = 0; +; int bar(int x); +; void foo(int a, int b, char* c) { +; if (a == 0) { +; XX += 1; +; } else { +; if (c == 0) +; XX += 2; +; } +; for(int i=0; i<b; i++) +; bar(XX); +; } + +@XX = dso_local local_unnamed_addr global i32 0, align 4 + +; Function Attrs: nounwind +define dso_local void @foo(i32 noundef %a, i32 noundef %b, i8* noundef readnone %c) local_unnamed_addr #0 { +; CHECK-LABEL: foo: +; CHECK: # %bb.0: # %entry +; CHECK-NEXT: pushq %rbx # encoding: [0x53] +; CHECK-NEXT: movl %esi, %ebx # encoding: [0x89,0xf3] +; CHECK-NEXT: testl %edi, %edi # encoding: [0x85,0xff] +; CHECK-NEXT: je .LBB0_1 # encoding: [0x74,A] +; CHECK-NEXT: # fixup A - offset: 1, value: .LBB0_1-1, kind: FK_PCRel_1 +; CHECK-NEXT: # %bb.2: # %if.else +; CHECK-NEXT: testq %rdx, %rdx # encoding: [0x48,0x85,0xd2] +; CHECK-NEXT: ds # encoding: [0x3e] +; CHECK-NEXT: jne .LBB0_5 # encoding: [0x75,A] +; CHECK-NEXT: # fixup A - offset: 1, value: .LBB0_5-1, kind: FK_PCRel_1 +; CHECK-NEXT: # %bb.3: +; CHECK-NEXT: movl $2, %eax # encoding: [0xb8,0x02,0x00,0x00,0x00] +; CHECK-NEXT: jmp .LBB0_4 # encoding: [0xeb,A] +; CHECK-NEXT: # fixup A - offset: 1, value: .LBB0_4-1, kind: FK_PCRel_1 +; CHECK-NEXT: .LBB0_1: +; CHECK-NEXT: movl $1, %eax # encoding: [0xb8,0x01,0x00,0x00,0x00] +; CHECK-NEXT: .LBB0_4: # %if.end4.sink.split +; CHECK-NEXT: addl %eax, XX(%rip) # encoding: [0x01,0x05,A,A,A,A] +; CHECK-NEXT: # fixup A - offset: 2, value: XX-4, kind: reloc_riprel_4byte +; CHECK-NEXT: .LBB0_5: # %if.end4 +; CHECK-NEXT: testl %ebx, %ebx # encoding: [0x85,0xdb] +; CHECK-NEXT: jle .LBB0_7 # encoding: [0x7e,A] +; CHECK-NEXT: # fixup A - offset: 1, value: .LBB0_7-1, kind: FK_PCRel_1 +; CHECK-NEXT: .p2align 4, 0x90 +; CHECK-NEXT: .LBB0_6: # %for.body +; CHECK-NEXT: # =>This Inner Loop Header: Depth=1 +; CHECK-NEXT: movl XX(%rip), %edi # encoding: [0x8b,0x3d,A,A,A,A] +; CHECK-NEXT: # fixup A - offset: 2, value: XX-4, kind: reloc_riprel_4byte_relax +; CHECK-NEXT: callq bar # encoding: [0xe8,A,A,A,A] +; CHECK-NEXT: # fixup A - offset: 1, value: bar-4, kind: reloc_branch_4byte_pcrel +; CHECK-NEXT: decl %ebx # encoding: [0xff,0xcb] +; CHECK-NEXT: ds # encoding: [0x3e] +; CHECK-NEXT: jne .LBB0_6 # encoding: [0x75,A] +; CHECK-NEXT: # fixup A - offset: 1, value: .LBB0_6-1, kind: FK_PCRel_1 +; CHECK-NEXT: .LBB0_7: # %for.cond.cleanup +; CHECK-NEXT: popq %rbx # encoding: [0x5b] +; CHECK-NEXT: retq # encoding: [0xc3] +entry: + %cmp = icmp eq i32 %a, 0 + br i1 %cmp, label %if.end4.sink.split, label %if.else + +if.else: ; preds = %entry + %cmp1 = icmp eq i8* %c, null + br i1 %cmp1, label %if.end4.sink.split, label %if.end4 + +if.end4.sink.split: ; preds = %if.else, %entry + %.sink10 = phi i32 [ 1, %entry ], [ 2, %if.else ] + %0 = load i32, i32* @XX, align 4 + %add3 = add nsw i32 %0, %.sink10 + store i32 %add3, i32* @XX, align 4 + br label %if.end4 + +if.end4: ; preds = %if.end4.sink.split, %if.else + %cmp58 = icmp sgt i32 %b, 0 + br i1 %cmp58, label %for.body, label %for.cond.cleanup + +for.cond.cleanup: ; preds = %for.body, %if.end4 + ret void + +for.body: ; preds = %if.end4, %for.body + %i.09 = phi i32 [ %inc, %for.body ], [ 0, %if.end4 ] + %1 = load i32, i32* @XX, align 4 + %call = tail call i32 @bar(i32 noundef %1) #0 + %inc = add nuw nsw i32 %i.09, 1 + %exitcond.not = icmp eq i32 %inc, %b + br i1 %exitcond.not, label %for.cond.cleanup, label %for.body +} + +declare dso_local i32 @bar(i32 noundef) local_unnamed_addr #0 + +attributes #0 = { nounwind "target-features"="+branch-hint" } `````````` </details> https://github.com/llvm/llvm-project/pull/97721 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
