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[SROA] Propagate no-signed-zeros(nsz) fast-math flag on the phi node …
…using function attribute (#83381) Its expected that the sequence `return X > 0.0 ? X : -X`, compiled with -Ofast, produces fabs intrinsic. However, at this point, LLVM is unable to do so. The above sequence goes through the following transformation during the pass pipeline: 1) SROA pass generates the phi node. Here, it does not infer the fast-math flags on the phi node unlike clang frontend typically does. 2) Phi node eventually gets translated into select instruction. Because of missing no-signed-zeros(nsz) fast-math flag on the select instruction, InstCombine pass fails to fold the sequence into fabs intrinsic. This patch, as a part of SROA, tries to propagate nsz fast-math flag on the phi node using function attribute enabling this folding. Closes #51601 Co-authored-by: Sushant Gokhale <sgokhale@nvidia.com>
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5 | ||
; RUN: opt -passes='default<O1>' -S < %s | FileCheck %s | ||
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; Following test must generate fabs intrinsic. It goes through following stages | ||
; 1. SROA propagates the nsz function attribute on the phi node. | ||
; 2. SimplifyCFG pass converts phi node to select. | ||
; 3. InstCombine converts select with nsz flag into fabs intrinsic. | ||
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define double @fabs_fcmp_olt_nsz_func_attr(double %0, double %1) "no-signed-zeros-fp-math"="true" { | ||
; CHECK-LABEL: define double @fabs_fcmp_olt_nsz_func_attr( | ||
; CHECK-SAME: double [[TMP0:%.*]], double [[TMP1:%.*]]) local_unnamed_addr #[[ATTR0:[0-9]+]] { | ||
; CHECK-NEXT: [[ENTRY:.*:]] | ||
; CHECK-NEXT: [[X_0:%.*]] = tail call nnan nsz double @llvm.fabs.f64(double [[TMP0]]) | ||
; CHECK-NEXT: ret double [[X_0]] | ||
entry: | ||
%x = alloca double | ||
store double %0, ptr %x | ||
%cmp = fcmp nnan nsz olt double %0, 0.000000e+00 | ||
br i1 %cmp, label %if.then, label %return | ||
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if.then: ; preds = %entry | ||
%fneg = fneg nnan nsz double %0 | ||
store double %fneg, ptr %x | ||
br label %return | ||
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return: ; preds = %entry, %if.then | ||
%ret = load double, ptr %x | ||
ret double %ret | ||
} |
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llvm/test/Transforms/SROA/propagate-fast-math-flags-on-phi.ll
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; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4 | ||
; RUN: opt < %s -passes='sroa' -S | FileCheck %s | ||
define double @phi_with_nsz(double %x) "no-signed-zeros-fp-math"="true" { | ||
; CHECK-LABEL: define double @phi_with_nsz( | ||
; CHECK-SAME: double [[X:%.*]]) #[[ATTR0:[0-9]+]] { | ||
; CHECK-NEXT: entry: | ||
; CHECK-NEXT: [[CMP:%.*]] = fcmp olt double [[X]], 0.000000e+00 | ||
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[RETURN:%.*]] | ||
; CHECK: if.then: | ||
; CHECK-NEXT: [[FNEG:%.*]] = fneg double [[X]] | ||
; CHECK-NEXT: br label [[RETURN]] | ||
; CHECK: return: | ||
; CHECK-NEXT: [[X_ADDR_0:%.*]] = phi nsz double [ [[FNEG]], [[IF_THEN]] ], [ undef, [[ENTRY:%.*]] ] | ||
; CHECK-NEXT: ret double [[X_ADDR_0]] | ||
entry: | ||
%x.addr = alloca double | ||
%cmp = fcmp olt double %x, 0.0 | ||
br i1 %cmp, label %if.then, label %return | ||
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if.then: ; preds = %entry | ||
%fneg = fneg double %x | ||
store double %fneg, ptr %x.addr | ||
br label %return | ||
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return: ; preds = %entry,%if.then | ||
%retval = load double, ptr %x.addr | ||
ret double %retval | ||
} | ||
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define <2 x double> @vector_phi_with_nsz(<2 x double> %x, i1 %cmp, <2 x double> %a, <2 x double> %b) "no-signed-zeros-fp-math"="true" { | ||
; CHECK-LABEL: define <2 x double> @vector_phi_with_nsz( | ||
; CHECK-SAME: <2 x double> [[X:%.*]], i1 [[CMP:%.*]], <2 x double> [[A:%.*]], <2 x double> [[B:%.*]]) #[[ATTR0]] { | ||
; CHECK-NEXT: entry: | ||
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[RETURN:%.*]] | ||
; CHECK: if.then: | ||
; CHECK-NEXT: br label [[RETURN]] | ||
; CHECK: return: | ||
; CHECK-NEXT: [[X_ADDR_0:%.*]] = phi nsz <2 x double> [ [[B]], [[IF_THEN]] ], [ [[A]], [[ENTRY:%.*]] ] | ||
; CHECK-NEXT: ret <2 x double> [[X_ADDR_0]] | ||
entry: | ||
%x.addr = alloca <2 x double> | ||
store <2 x double> %a, ptr %x.addr | ||
br i1 %cmp, label %if.then, label %return | ||
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if.then: ; preds = %entry | ||
store <2 x double> %b, ptr %x.addr | ||
br label %return | ||
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return: ; preds = %entry,%if.then | ||
%retval = load <2 x double>, ptr %x.addr | ||
ret <2 x double> %retval | ||
} | ||
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define double @phi_without_nsz(double %x) "no-signed-zeros-fp-math"="false" { | ||
; CHECK-LABEL: define double @phi_without_nsz( | ||
; CHECK-SAME: double [[X:%.*]]) #[[ATTR1:[0-9]+]] { | ||
; CHECK-NEXT: entry: | ||
; CHECK-NEXT: [[CMP:%.*]] = fcmp olt double [[X]], 0.000000e+00 | ||
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[RETURN:%.*]] | ||
; CHECK: if.then: | ||
; CHECK-NEXT: [[FNEG:%.*]] = fneg double [[X]] | ||
; CHECK-NEXT: br label [[RETURN]] | ||
; CHECK: return: | ||
; CHECK-NEXT: [[X_ADDR_0:%.*]] = phi double [ [[FNEG]], [[IF_THEN]] ], [ undef, [[ENTRY:%.*]] ] | ||
; CHECK-NEXT: ret double [[X_ADDR_0]] | ||
entry: | ||
%x.addr = alloca double | ||
%cmp = fcmp olt double %x, 0.0 | ||
br i1 %cmp, label %if.then, label %return | ||
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if.then: ; preds = %entry | ||
%fneg = fneg double %x | ||
store double %fneg, ptr %x.addr | ||
br label %return | ||
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return: ; preds = %entry,%if.then | ||
%retval = load double, ptr %x.addr | ||
ret double %retval | ||
} |