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[LoopVectorize] Don't emit remarks about lack of scalable vectors unless they're specifically requested. 

Previously we emitted a "does not support scalable vectors"
remark for all targets whenever vectorisation is attempted. This
pollutes the output for architectures that don't support scalable
vectors and is likely confusing to the user.

Instead this patch introduces a debug message that reports when
scalable vectorisation is allowed by the target and only issues
the previous remark when scalable vectorisation is specifically
requested, for example:

  #pragma clang loop vectorize_width(2, scalable)

Differential Revision: https://reviews.llvm.org/D108028
This commit is contained in:
Paul Walker 2021-08-13 12:47:51 +01:00
parent 81b106584f
commit f7a831daa6
3 changed files with 50 additions and 32 deletions
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46
llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@ -5591,13 +5591,8 @@ bool LoopVectorizationCostModel::runtimeChecksRequired() {
ElementCount
LoopVectorizationCostModel::getMaxLegalScalableVF(unsigned MaxSafeElements) {
if (!TTI.supportsScalableVectors() && !ForceTargetSupportsScalableVectors) {
reportVectorizationInfo(
"Disabling scalable vectorization, because target does not "
"support scalable vectors.",
"ScalableVectorsUnsupported", ORE, TheLoop);
if (!TTI.supportsScalableVectors() && !ForceTargetSupportsScalableVectors)
return ElementCount::getScalable(0);
}
if (Hints->isScalableVectorizationDisabled()) {
reportVectorizationInfo("Scalable vectorization is explicitly disabled",
@ -5605,6 +5600,8 @@ LoopVectorizationCostModel::getMaxLegalScalableVF(unsigned MaxSafeElements) {
return ElementCount::getScalable(0);
}
LLVM_DEBUG(dbgs() << "LV: Scalable vectorization is available\n");
auto MaxScalableVF = ElementCount::getScalable(
std::numeric_limits<ElementCount::ScalarTy>::max());
@ -5707,17 +5704,32 @@ LoopVectorizationCostModel::computeFeasibleMaxVF(unsigned ConstTripCount,
return MaxSafeFixedVF;
}
LLVM_DEBUG(dbgs() << "LV: User VF=" << UserVF
<< " is unsafe. Ignoring scalable UserVF.\n");
ORE->emit([&]() {
return OptimizationRemarkAnalysis(DEBUG_TYPE, "VectorizationFactor",
TheLoop->getStartLoc(),
TheLoop->getHeader())
<< "User-specified vectorization factor "
<< ore::NV("UserVectorizationFactor", UserVF)
<< " is unsafe. Ignoring the hint to let the compiler pick a "
"suitable VF.";
});
if (!TTI.supportsScalableVectors() && !ForceTargetSupportsScalableVectors) {
LLVM_DEBUG(dbgs() << "LV: User VF=" << UserVF
<< " is ignored because scalable vectors are not "
"available.\n");
ORE->emit([&]() {
return OptimizationRemarkAnalysis(DEBUG_TYPE, "VectorizationFactor",
TheLoop->getStartLoc(),
TheLoop->getHeader())
<< "User-specified vectorization factor "
<< ore::NV("UserVectorizationFactor", UserVF)
<< " is ignored because the target does not support scalable "
"vectors. The compiler will pick a more suitable value.";
});
} else {
LLVM_DEBUG(dbgs() << "LV: User VF=" << UserVF
<< " is unsafe. Ignoring scalable UserVF.\n");
ORE->emit([&]() {
return OptimizationRemarkAnalysis(DEBUG_TYPE, "VectorizationFactor",
TheLoop->getStartLoc(),
TheLoop->getHeader())
<< "User-specified vectorization factor "
<< ore::NV("UserVectorizationFactor", UserVF)
<< " is unsafe. Ignoring the hint to let the compiler pick a "
"more suitable value.";
});
}
}
LLVM_DEBUG(dbgs() << "LV: The Smallest and Widest types: " << SmallestType

32
llvm/test/Transforms/LoopVectorize/AArch64/scalable-vf-hint.ll
View File

@ -38,6 +38,7 @@ target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
; fixed-width vectorization is used instead.
; CHECK-DBG: LV: Checking a loop in "test1"
; CHECK-DBG: LV: Scalable vectorization is available
; CHECK-DBG: LV: Max legal vector width too small, scalable vectorization unfeasible.
; CHECK-DBG: remark: <unknown>:0:0: Max legal vector width too small, scalable vectorization unfeasible.
; CHECK-DBG: LV: The max safe fixed VF is: 8.
@ -82,6 +83,7 @@ exit:
; }
; CHECK-DBG: LV: Checking a loop in "test2"
; CHECK-DBG: LV: Scalable vectorization is available
; CHECK-DBG: LV: Max legal vector width too small, scalable vectorization unfeasible.
; CHECK-DBG: LV: The max safe fixed VF is: 4.
; CHECK-DBG: LV: User VF=vscale x 8 is unsafe. Ignoring scalable UserVF.
@ -131,6 +133,7 @@ exit:
; Max fixed VF=32, Max scalable VF=2, safe to vectorize.
; CHECK-DBG-LABEL: LV: Checking a loop in "test3"
; CHECK-DBG: LV: Scalable vectorization is available
; CHECK-DBG: LV: The max safe scalable VF is: vscale x 2.
; CHECK-DBG: LV: Using user VF vscale x 2.
; CHECK-LABEL: @test3
@ -179,9 +182,10 @@ exit:
; Max fixed VF=32, Max scalable VF=2, unsafe to vectorize.
; CHECK-DBG-LABEL: LV: Checking a loop in "test4"
; CHECK-DBG: LV: Scalable vectorization is available
; CHECK-DBG: LV: The max safe scalable VF is: vscale x 2.
; CHECK-DBG: LV: User VF=vscale x 4 is unsafe. Ignoring scalable UserVF.
; CHECK-DBG: remark: <unknown>:0:0: User-specified vectorization factor vscale x 4 is unsafe. Ignoring the hint to let the compiler pick a suitable VF.
; CHECK-DBG: remark: <unknown>:0:0: User-specified vectorization factor vscale x 4 is unsafe. Ignoring the hint to let the compiler pick a more suitable value.
; CHECK-DBG: Found feasible scalable VF = vscale x 2
; CHECK-DBG: LV: Selecting VF: 4.
; CHECK-LABEL: @test4
@ -229,6 +233,7 @@ exit:
; Max fixed VF=128, Max scalable VF=8, safe to vectorize.
; CHECK-DBG-LABEL: LV: Checking a loop in "test5"
; CHECK-DBG: LV: Scalable vectorization is available
; CHECK-DBG: LV: The max safe scalable VF is: vscale x 8.
; CHECK-DBG: LV: Using user VF vscale x 4
; CHECK-LABEL: @test5
@ -276,13 +281,14 @@ exit:
; Max fixed VF=128, Max scalable VF=8, unsafe to vectorize.
; CHECK-DBG-LABEL: LV: Checking a loop in "test6"
; CHECK-DBG: LV: Scalable vectorization is available
; CHECK-DBG: LV: The max safe scalable VF is: vscale x 8.
; CHECK-DBG: LV: User VF=vscale x 16 is unsafe. Ignoring scalable UserVF.
; CHECK-DBG: remark: <unknown>:0:0: User-specified vectorization factor vscale x 16 is unsafe. Ignoring the hint to let the compiler pick a suitable VF.
; CHECK-DBG: remark: <unknown>:0:0: User-specified vectorization factor vscale x 16 is unsafe. Ignoring the hint to let the compiler pick a more suitable value.
; CHECK-DBG: LV: Found feasible scalable VF = vscale x 4
; CHECK-DBG: Selecting VF: 4.
; CHECK-DBG: Selecting VF: vscale x 4.
; CHECK-LABEL: @test6
; CHECK: <4 x i32>
; CHECK: <vscale x 4 x i32>
define void @test6(i32* %a, i32* %b) {
entry:
br label %loop
@ -310,9 +316,8 @@ exit:
!17 = !{!"llvm.loop.vectorize.scalable.enable", i1 true}
; CHECK-NO-SVE-REMARKS-LABEL: LV: Checking a loop in "test_no_sve"
; CHECK-NO-SVE-REMARKS: LV: Disabling scalable vectorization, because target does not support scalable vectors.
; CHECK-NO-SVE-REMARKS: remark: <unknown>:0:0: Disabling scalable vectorization, because target does not support scalable vectors.
; CHECK-NO-SVE-REMARKS: LV: User VF=vscale x 4 is unsafe. Ignoring scalable UserVF.
; CHECK-NO-SVE-REMARKS: LV: User VF=vscale x 4 is ignored because scalable vectors are not available.
; CHECK-NO-SVE-REMARKS: remark: <unknown>:0:0: User-specified vectorization factor vscale x 4 is ignored because the target does not support scalable vectors. The compiler will pick a more suitable value.
; CHECK-NO-SVE-REMARKS: LV: Selecting VF: 4.
; CHECK-NO-SVE-LABEL: @test_no_sve
; CHECK-NO-SVE: <4 x i32>
@ -344,12 +349,13 @@ exit:
; Test the LV falls back to fixed-width vectorization if scalable vectors are
; supported but max vscale is undefined.
;
; CHECK-NO-SVE-REMARKS-LABEL: LV: Checking a loop in "test_no_max_vscale"
; CHECK-NO-SVE-REMARKS: The max safe fixed VF is: 4.
; CHECK-NO-SVE-REMARKS: LV: User VF=vscale x 4 is unsafe. Ignoring scalable UserVF.
; CHECK-NO-SVE-REMARKS: LV: Selecting VF: 4.
; CHECK-NO-SVE-LABEL: @test_no_max_vscale
; CHECK-NO-SVE: <4 x i32>
; CHECK-DBG-LABEL: LV: Checking a loop in "test_no_max_vscale"
; CHECK-DBG: LV: Scalable vectorization is available
; CHECK-DBG: The max safe fixed VF is: 4.
; CHECK-DBG: LV: User VF=vscale x 4 is unsafe. Ignoring scalable UserVF.
; CHECK-DBG: LV: Selecting VF: 4.
; CHECK-LABEL: @test_no_max_vscale
; CHECK: <4 x i32>
define void @test_no_max_vscale(i32* %a, i32* %b) {
entry:
br label %loop

4
llvm/test/Transforms/LoopVectorize/scalable-vf-hint.ll
View File

@ -3,8 +3,8 @@
target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
; CHECK: LV: Disabling scalable vectorization, because target does not support scalable vectors.
; CHECK: remark: <unknown>:0:0: Disabling scalable vectorization, because target does not support scalable vectors.
; CHECK: LV: User VF=vscale x 4 is ignored because scalable vectors are not available.
; CHECK: remark: <unknown>:0:0: User-specified vectorization factor vscale x 4 is ignored because the target does not support scalable vectors. The compiler will pick a more suitable value.
; CHECK: LV: The Widest register safe to use is: 32 bits.
define void @test1(i32* %a, i32* %b) {
entry: