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Demote(B)Float16 pass: only keep enabled for PPC. #55486

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Aug 17, 2024
Merged

Demote(B)Float16 pass: only keep enabled for PPC. #55486

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47 changes: 19 additions & 28 deletions src/llvm-demote-float16.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -49,37 +49,28 @@ extern JuliaOJIT *jl_ExecutionEngine;

namespace {

static bool have_fp16(Function &caller, const Triple &TT) {
Attribute FSAttr = caller.getFnAttribute("target-features");
StringRef FS = "";
if (FSAttr.isValid())
FS = FSAttr.getValueAsString();
else if (jl_ExecutionEngine)
FS = jl_ExecutionEngine->getTargetFeatureString();
// else probably called from opt, just do nothing
if (TT.isAArch64()) {
if (FS.find("+fp16fml") != llvm::StringRef::npos || FS.find("+fullfp16") != llvm::StringRef::npos){
return true;
}
} else if (TT.getArch() == Triple::x86_64) {
if (FS.find("+avx512fp16") != llvm::StringRef::npos){
return true;
}
}
if (caller.hasFnAttribute("julia.hasfp16")) {
return true;
}
return false;
static bool have_fp16(Function &F, const Triple &TT) {
// for testing purposes
Attribute Attr = F.getFnAttribute("julia.hasfp16");
if (Attr.isValid())
return Attr.getValueAsBool();

// llvm/llvm-project#97975: on some platforms, `half` uses excessive precision
if (TT.isPPC())
return false;

return true;
}

static bool have_bf16(Function &caller, const Triple &TT) {
if (caller.hasFnAttribute("julia.hasbf16")) {
return true;
}
static bool have_bf16(Function &F, const Triple &TT) {
// for testing purposes
Attribute Attr = F.getFnAttribute("julia.hasbf16");
if (Attr.isValid())
return Attr.getValueAsBool();

// there's no targets that fully support bfloat yet;,
// AVX512BF16 only provides conversion and dot product instructions.
return false;
// https://github.com/llvm/llvm-project/issues/97975#issuecomment-2218770199:
// on current versions of LLVM, bf16 always uses TypeSoftPromoteHalf
return true;
}

static bool demoteFloat16(Function &F)
Expand Down
26 changes: 0 additions & 26 deletions test/llvmpasses/fastmath.jl
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Expand Up @@ -16,29 +16,3 @@ import Base.FastMath

# CHECK: call fast float @llvm.sqrt.f32(float %"x::Float32")
emit(FastMath.sqrt_fast, Float32)


# Float16 operations should be performed as Float32, unless @fastmath is specified
# TODO: this is not true for platforms that natively support Float16

foo(x::T,y::T) where T = x-y == zero(T)
# CHECK: define {{(swiftcc )?}}i8 @julia_foo_{{[0-9]+}}({{.*}}half %[[X:"x::Float16"]], half %[[Y:"y::Float16"]]) {{.*}}{
# CHECK-DAG: %[[XEXT:[0-9]+]] = fpext half %[[X]] to float
# CHECK-DAG: %[[YEXT:[0-9]+]] = fpext half %[[Y]] to float
# CHECK: %[[DIFF:[0-9]+]] = fsub float %[[XEXT]], %[[YEXT]]
# CHECK: %[[TRUNC:[0-9]+]] = fptrunc float %[[DIFF]] to half
# CHECK: %[[DIFFEXT:[0-9]+]] = fpext half %[[TRUNC]] to float
# CHECK: %[[CMP:[0-9]+]] = fcmp oeq float %[[DIFFEXT]], 0.000000e+00
# CHECK: %[[ZEXT:[0-9]+]] = zext i1 %[[CMP]] to i8
# CHECK: ret i8 %[[ZEXT]]
# CHECK: }
emit(foo, Float16, Float16)

@fastmath foo(x::T,y::T) where T = x-y == zero(T)
# CHECK: define {{(swiftcc )?}}i8 @julia_foo_{{[0-9]+}}({{.*}}half %[[X:"x::Float16"]], half %[[Y:"y::Float16"]]) {{.*}}{
# CHECK: %[[DIFF:[0-9]+]] = fsub fast half %[[X]], %[[Y]]
# CHECK: %[[CMP:[0-9]+]] = fcmp fast oeq half %[[DIFF]], 0xH0000
# CHECK: %[[ZEXT:[0-9]+]] = zext i1 %[[CMP]] to i8
# CHECK: ret i8 %[[ZEXT]]
# CHECK: }
emit(foo, Float16, Float16)
71 changes: 68 additions & 3 deletions test/llvmpasses/float16.ll
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Expand Up @@ -99,7 +99,7 @@ top:
ret half %13
}

define bfloat @demote_bfloat_test(bfloat %a, bfloat %b) {
define bfloat @demote_bfloat_test(bfloat %a, bfloat %b) #2 {
top:
; CHECK-LABEL: @demote_bfloat_test(
; CHECK-NEXT: top:
Expand Down Expand Up @@ -160,5 +160,70 @@ top:
ret bfloat %13
}

attributes #0 = { "target-features"="-avx512fp16" }
attributes #1 = { "target-features"="+avx512fp16" }
define bfloat @native_bfloat_test(bfloat %a, bfloat %b) #3 {
top:
; CHECK-LABEL: @native_bfloat_test(
; CHECK-NEXT: top:
; CHECK-NEXT: %0 = fadd bfloat %a, %b
; CHECK-NEXT: %1 = fadd bfloat %0, %b
; CHECK-NEXT: %2 = fadd bfloat %1, %b
; CHECK-NEXT: %3 = fmul bfloat %2, %b
; CHECK-NEXT: %4 = fdiv bfloat %3, %b
; CHECK-NEXT: %5 = insertelement <2 x bfloat> undef, bfloat %a, i32 0
; CHECK-NEXT: %6 = insertelement <2 x bfloat> %5, bfloat %b, i32 1
; CHECK-NEXT: %7 = insertelement <2 x bfloat> undef, bfloat %b, i32 0
; CHECK-NEXT: %8 = insertelement <2 x bfloat> %7, bfloat %b, i32 1
; CHECK-NEXT: %9 = fadd <2 x bfloat> %6, %8
; CHECK-NEXT: %10 = extractelement <2 x bfloat> %9, i32 0
; CHECK-NEXT: %11 = extractelement <2 x bfloat> %9, i32 1
; CHECK-NEXT: %12 = fadd bfloat %10, %11
; CHECK-NEXT: %13 = fadd bfloat %12, %4
; CHECK-NEXT: ret bfloat %13
;
%0 = fadd bfloat %a, %b
%1 = fadd bfloat %0, %b
%2 = fadd bfloat %1, %b
%3 = fmul bfloat %2, %b
%4 = fdiv bfloat %3, %b
%5 = insertelement <2 x bfloat> undef, bfloat %a, i32 0
%6 = insertelement <2 x bfloat> %5, bfloat %b, i32 1
%7 = insertelement <2 x bfloat> undef, bfloat %b, i32 0
%8 = insertelement <2 x bfloat> %7, bfloat %b, i32 1
%9 = fadd <2 x bfloat> %6, %8
%10 = extractelement <2 x bfloat> %9, i32 0
%11 = extractelement <2 x bfloat> %9, i32 1
%12 = fadd bfloat %10, %11
%13 = fadd bfloat %12, %4
ret bfloat %13
}

define i1 @fast_half_test(half %0, half %1) #0 {
top:
; CHECK-LABEL: @fast_half_test(
; CHECK-NEXT: top:
; CHECK-NEXT: %2 = fsub fast half %0, %1
; CHECK-NEXT: %3 = fcmp fast oeq half %2, 0xH0000
; CHECK-NEXT: ret i1 %3
;
%2 = fsub fast half %0, %1
%3 = fcmp fast oeq half %2, 0xH0000
ret i1 %3
}

define i1 @fast_bfloat_test(bfloat %0, bfloat %1) #2 {
top:
; CHECK-LABEL: @fast_bfloat_test(
; CHECK-NEXT: top:
; CHECK-NEXT: %2 = fsub fast bfloat %0, %1
; CHECK-NEXT: %3 = fcmp fast oeq bfloat %2, 0xR0000
; CHECK-NEXT: ret i1 %3
;
%2 = fsub fast bfloat %0, %1
%3 = fcmp fast oeq bfloat %2, 0xR0000
ret i1 %3
}

attributes #0 = { "julia.hasfp16"="false" }
attributes #1 = { "julia.hasfp16"="true" }
attributes #2 = { "julia.hasbf16"="false" }
attributes #3 = { "julia.hasbf16"="true" }