[llvm] r324255 - [InstCombine] add unsigned saturation subtraction canonicalizations
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 5 09:53:29 PST 2018
Author: spatel
Date: Mon Feb 5 09:53:29 2018
New Revision: 324255
URL: http://llvm.org/viewvc/llvm-project?rev=324255&view=rev
Log:
[InstCombine] add unsigned saturation subtraction canonicalizations
This is the instcombine part of unsigned saturation canonicalization.
Backend patches already commited:
https://reviews.llvm.org/D37510
https://reviews.llvm.org/D37534
It converts unsigned saturated subtraction patterns to forms recognized
by the backend:
(a > b) ? a - b : 0 -> ((a > b) ? a : b) - b)
(b < a) ? a - b : 0 -> ((a > b) ? a : b) - b)
(b > a) ? 0 : a - b -> ((a > b) ? a : b) - b)
(a < b) ? 0 : a - b -> ((a > b) ? a : b) - b)
((a > b) ? b - a : 0) -> - ((a > b) ? a : b) - b)
((b < a) ? b - a : 0) -> - ((a > b) ? a : b) - b)
((b > a) ? 0 : b - a) -> - ((a > b) ? a : b) - b)
((a < b) ? 0 : b - a) -> - ((a > b) ? a : b) - b)
Patch by Yulia Koval!
Differential Revision: https://reviews.llvm.org/D41480
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
llvm/trunk/test/Transforms/InstCombine/unsigned_saturated_sub.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp?rev=324255&r1=324254&r2=324255&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp Mon Feb 5 09:53:29 2018
@@ -538,6 +538,59 @@ static Value *foldSelectICmpAndOr(const
return Builder.CreateOr(V, Y);
}
+/// Transform patterns such as: (a > b) ? a - b : 0
+/// into: ((a > b) ? a : b) - b)
+/// This produces a canonical max pattern that is more easily recognized by the
+/// backend and converted into saturated subtraction instructions if those
+/// exist.
+/// There are 8 commuted/swapped variants of this pattern.
+/// TODO: Also support a - UMIN(a,b) patterns.
+static Value *canonicalizeSaturatedSubtract(const ICmpInst *ICI,
+ const Value *TrueVal,
+ const Value *FalseVal,
+ InstCombiner::BuilderTy &Builder) {
+ ICmpInst::Predicate Pred = ICI->getPredicate();
+ if (!ICmpInst::isUnsigned(Pred))
+ return nullptr;
+
+ // (b > a) ? 0 : a - b -> (b <= a) ? a - b : 0
+ if (match(TrueVal, m_Zero())) {
+ Pred = ICmpInst::getInversePredicate(Pred);
+ std::swap(TrueVal, FalseVal);
+ }
+ if (!match(FalseVal, m_Zero()))
+ return nullptr;
+
+ Value *A = ICI->getOperand(0);
+ Value *B = ICI->getOperand(1);
+ if (Pred == ICmpInst::ICMP_ULE || Pred == ICmpInst::ICMP_ULT) {
+ // (b < a) ? a - b : 0 -> (a > b) ? a - b : 0
+ std::swap(A, B);
+ Pred = ICmpInst::getSwappedPredicate(Pred);
+ }
+
+ assert((Pred == ICmpInst::ICMP_UGE || Pred == ICmpInst::ICMP_UGT) &&
+ "Unexpected isUnsigned predicate!");
+
+ // Account for swapped form of subtraction: ((a > b) ? b - a : 0).
+ bool IsNegative = false;
+ if (match(TrueVal, m_Sub(m_Specific(B), m_Specific(A))))
+ IsNegative = true;
+ else if (!match(TrueVal, m_Sub(m_Specific(A), m_Specific(B))))
+ return nullptr;
+
+ // If sub is used anywhere else, we wouldn't be able to eliminate it
+ // afterwards.
+ if (!TrueVal->hasOneUse())
+ return nullptr;
+
+ // All checks passed, convert to canonical unsigned saturated subtraction
+ // form: sub(max()).
+ // (a > b) ? a - b : 0 -> ((a > b) ? a : b) - b)
+ Value *Max = Builder.CreateSelect(Builder.CreateICmp(Pred, A, B), A, B);
+ return IsNegative ? Builder.CreateSub(B, Max) : Builder.CreateSub(Max, B);
+}
+
/// Attempt to fold a cttz/ctlz followed by a icmp plus select into a single
/// call to cttz/ctlz with flag 'is_zero_undef' cleared.
///
@@ -860,10 +913,12 @@ Instruction *InstCombiner::foldSelectIns
if (Value *V = foldSelectCttzCtlz(ICI, TrueVal, FalseVal, Builder))
return replaceInstUsesWith(SI, V);
+ if (Value *V = canonicalizeSaturatedSubtract(ICI, TrueVal, FalseVal, Builder))
+ return replaceInstUsesWith(SI, V);
+
return Changed ? &SI : nullptr;
}
-
/// SI is a select whose condition is a PHI node (but the two may be in
/// different blocks). See if the true/false values (V) are live in all of the
/// predecessor blocks of the PHI. For example, cases like this can't be mapped:
Modified: llvm/trunk/test/Transforms/InstCombine/unsigned_saturated_sub.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/unsigned_saturated_sub.ll?rev=324255&r1=324254&r2=324255&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/unsigned_saturated_sub.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/unsigned_saturated_sub.ll Mon Feb 5 09:53:29 2018
@@ -12,10 +12,10 @@ declare void @use(i64)
define i64 @max_sub_ugt(i64 %a, i64 %b) {
; CHECK-LABEL: @max_sub_ugt(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[A]], [[B]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i64 [[SUB]], i64 0
-; CHECK-NEXT: ret i64 [[SEL]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ugt i64 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[A]], i64 [[B]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[TMP2]], [[B]]
+; CHECK-NEXT: ret i64 [[TMP3]]
;
%cmp = icmp ugt i64 %a, %b
%sub = sub i64 %a, %b
@@ -23,15 +23,30 @@ define i64 @max_sub_ugt(i64 %a, i64 %b)
ret i64 %sel
}
+; (a >= b) ? a - b : 0 -> ((a >= b) ? a : b) - b)
+
+define i64 @max_sub_uge(i64 %a, i64 %b) {
+; CHECK-LABEL: @max_sub_uge(
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[B]], i64 [[A]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[TMP2]], [[B]]
+; CHECK-NEXT: ret i64 [[TMP3]]
+;
+ %cmp = icmp uge i64 %a, %b
+ %sub = sub i64 %a, %b
+ %sel = select i1 %cmp, i64 %sub ,i64 0
+ ret i64 %sel
+}
+
; Again, with vectors:
; (a > b) ? a - b : 0 -> ((a > b) ? a : b) - b)
define <4 x i32> @max_sub_ugt_vec(<4 x i32> %a, <4 x i32> %b) {
; CHECK-LABEL: @max_sub_ugt_vec(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ugt <4 x i32> [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub <4 x i32> [[A]], [[B]]
-; CHECK-NEXT: [[SEL:%.*]] = select <4 x i1> [[CMP]], <4 x i32> [[SUB]], <4 x i32> zeroinitializer
-; CHECK-NEXT: ret <4 x i32> [[SEL]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ugt <4 x i32> [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[A]], <4 x i32> [[B]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub <4 x i32> [[TMP2]], [[B]]
+; CHECK-NEXT: ret <4 x i32> [[TMP3]]
;
%cmp = icmp ugt <4 x i32> %a, %b
%sub = sub <4 x i32> %a, %b
@@ -44,12 +59,12 @@ define <4 x i32> @max_sub_ugt_vec(<4 x i
define i64 @max_sub_ult(i64 %a, i64 %b) {
; CHECK-LABEL: @max_sub_ult(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[B:%.*]], [[A:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[A]], [[B]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i64 [[SUB]], i64 0
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[B:%.*]], [[A:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[A]], i64 [[B]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[TMP2]], [[B]]
; CHECK-NEXT: [[EXTRASUB:%.*]] = sub i64 [[B]], [[A]]
; CHECK-NEXT: call void @use(i64 [[EXTRASUB]])
-; CHECK-NEXT: ret i64 [[SEL]]
+; CHECK-NEXT: ret i64 [[TMP3]]
;
%cmp = icmp ult i64 %b, %a
%sub = sub i64 %a, %b
@@ -63,12 +78,12 @@ define i64 @max_sub_ult(i64 %a, i64 %b)
define i64 @max_sub_ugt_sel_swapped(i64 %a, i64 %b) {
; CHECK-LABEL: @max_sub_ugt_sel_swapped(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[B:%.*]], [[A:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[A]], [[B]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i64 0, i64 [[SUB]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ugt i64 [[B:%.*]], [[A:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[B]], i64 [[A]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[TMP2]], [[B]]
; CHECK-NEXT: [[EXTRASUB:%.*]] = sub i64 [[B]], [[A]]
; CHECK-NEXT: call void @use(i64 [[EXTRASUB]])
-; CHECK-NEXT: ret i64 [[SEL]]
+; CHECK-NEXT: ret i64 [[TMP3]]
;
%cmp = icmp ugt i64 %b, %a
%sub = sub i64 %a, %b
@@ -82,10 +97,10 @@ define i64 @max_sub_ugt_sel_swapped(i64
define i64 @max_sub_ult_sel_swapped(i64 %a, i64 %b) {
; CHECK-LABEL: @max_sub_ult_sel_swapped(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[A]], [[B]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i64 0, i64 [[SUB]]
-; CHECK-NEXT: ret i64 [[SEL]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[B]], i64 [[A]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[TMP2]], [[B]]
+; CHECK-NEXT: ret i64 [[TMP3]]
;
%cmp = icmp ult i64 %a, %b
%sub = sub i64 %a, %b
@@ -97,12 +112,12 @@ define i64 @max_sub_ult_sel_swapped(i64
define i64 @neg_max_sub_ugt(i64 %a, i64 %b) {
; CHECK-LABEL: @neg_max_sub_ugt(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[B]], [[A]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i64 [[SUB]], i64 0
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ugt i64 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[A]], i64 [[B]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[B]], [[TMP2]]
; CHECK-NEXT: [[EXTRASUB:%.*]] = sub i64 [[A]], [[B]]
; CHECK-NEXT: call void @use(i64 [[EXTRASUB]])
-; CHECK-NEXT: ret i64 [[SEL]]
+; CHECK-NEXT: ret i64 [[TMP3]]
;
%cmp = icmp ugt i64 %a, %b
%sub = sub i64 %b, %a
@@ -116,10 +131,10 @@ define i64 @neg_max_sub_ugt(i64 %a, i64
define i64 @neg_max_sub_ult(i64 %a, i64 %b) {
; CHECK-LABEL: @neg_max_sub_ult(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[B:%.*]], [[A:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[B]], [[A]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i64 [[SUB]], i64 0
-; CHECK-NEXT: ret i64 [[SEL]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ugt i64 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[A]], i64 [[B]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[B]], [[TMP2]]
+; CHECK-NEXT: ret i64 [[TMP3]]
;
%cmp = icmp ult i64 %b, %a
%sub = sub i64 %b, %a
@@ -131,10 +146,10 @@ define i64 @neg_max_sub_ult(i64 %a, i64
define i64 @neg_max_sub_ugt_sel_swapped(i64 %a, i64 %b) {
; CHECK-LABEL: @neg_max_sub_ugt_sel_swapped(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[B:%.*]], [[A:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[B]], [[A]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i64 0, i64 [[SUB]]
-; CHECK-NEXT: ret i64 [[SEL]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[B]], i64 [[A]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[B]], [[TMP2]]
+; CHECK-NEXT: ret i64 [[TMP3]]
;
%cmp = icmp ugt i64 %b, %a
%sub = sub i64 %b, %a
@@ -146,12 +161,12 @@ define i64 @neg_max_sub_ugt_sel_swapped(
define i64 @neg_max_sub_ult_sel_swapped(i64 %a, i64 %b) {
; CHECK-LABEL: @neg_max_sub_ult_sel_swapped(
-; CHECK-NEXT: [[CMP:%.*]] = icmp ult i64 [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[B]], [[A]]
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i64 0, i64 [[SUB]]
+; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i64 [[B]], i64 [[A]]
+; CHECK-NEXT: [[TMP3:%.*]] = sub i64 [[B]], [[TMP2]]
; CHECK-NEXT: [[EXTRASUB:%.*]] = sub i64 [[A]], [[B]]
; CHECK-NEXT: call void @use(i64 [[EXTRASUB]])
-; CHECK-NEXT: ret i64 [[SEL]]
+; CHECK-NEXT: ret i64 [[TMP3]]
;
%cmp = icmp ult i64 %a, %b
%sub = sub i64 %b, %a
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