Skip to content

Commit

Permalink
[ValueTracking][InstSimplify] Support min/max selects in computeConst…
Browse files Browse the repository at this point in the history
…antRange()

Add support for min/max flavor selects in computeConstantRange(),
which allows us to fold comparisons of a min/max against a constant
in InstSimplify. This was suggested by spatel as an alternative
approach to D59378. I've also added the infinite looping test from
that revision here.

Differential Revision: https://reviews.llvm.org/D59506

llvm-svn: 356415
  • Loading branch information
nikic committed Mar 18, 2019
1 parent 930341b commit 106f0cd
Showing 3 changed files with 57 additions and 17 deletions.
23 changes: 22 additions & 1 deletion llvm/lib/Analysis/ValueTracking.cpp
Original file line number Diff line number Diff line change
@@ -5680,7 +5680,28 @@ static void setLimitsForSelectPattern(const SelectInst &SI, APInt &Lower,
return;
}

// TODO Handle min/max flavors.
const APInt *C;
if (!match(LHS, m_APInt(C)) && !match(RHS, m_APInt(C)))
return;

switch (R.Flavor) {
case SPF_UMIN:
Upper = *C + 1;
break;
case SPF_UMAX:
Lower = *C;
break;
case SPF_SMIN:
Lower = APInt::getSignedMinValue(BitWidth);
Upper = *C + 1;
break;
case SPF_SMAX:
Lower = *C;
Upper = APInt::getSignedMaxValue(BitWidth) + 1;
break;
default:
break;
}
}

ConstantRange llvm::computeConstantRange(const Value *V, bool UseInstrInfo) {
31 changes: 31 additions & 0 deletions llvm/test/Transforms/InstCombine/minmax-fold.ll
Original file line number Diff line number Diff line change
@@ -533,6 +533,37 @@ define i32 @clamp_check_for_no_infinite_loop2(i32 %i) {
ret i32 %res
}

; Check that there is no infinite loop because of reverse cmp transformation:
; (icmp slt smax(PositiveA, B) 2) -> (icmp eq B 1)
define i32 @clamp_check_for_no_infinite_loop3(i32 %i) {
; CHECK-LABEL: @clamp_check_for_no_infinite_loop3(
; CHECK-NEXT: [[I2:%.*]] = icmp sgt i32 [[I:%.*]], 1
; CHECK-NEXT: [[I3:%.*]] = select i1 [[I2]], i32 [[I]], i32 1
; CHECK-NEXT: br i1 true, label [[TRUELABEL:%.*]], label [[FALSELABEL:%.*]]
; CHECK: truelabel:
; CHECK-NEXT: [[I5:%.*]] = icmp slt i32 [[I3]], 2
; CHECK-NEXT: [[I6:%.*]] = select i1 [[I5]], i32 [[I3]], i32 2
; CHECK-NEXT: [[I7:%.*]] = shl nuw nsw i32 [[I6]], 2
; CHECK-NEXT: ret i32 [[I7]]
; CHECK: falselabel:
; CHECK-NEXT: ret i32 0
;

%i2 = icmp sgt i32 %i, 1
%i3 = select i1 %i2, i32 %i, i32 1
%i4 = icmp sgt i32 %i3, 0
br i1 %i4, label %truelabel, label %falselabel

truelabel: ; %i<=1, %i3>0
%i5 = icmp slt i32 %i3, 2
%i6 = select i1 %i5, i32 %i3, i32 2
%i7 = shl nuw nsw i32 %i6, 2
ret i32 %i7

falselabel:
ret i32 0
}

; The next 3 min tests should canonicalize to the same form...and not infinite loop.

define double @PR31751_umin1(i32 %x) {
20 changes: 4 additions & 16 deletions llvm/test/Transforms/InstSimplify/cmp_of_min_max.ll
Original file line number Diff line number Diff line change
@@ -3,10 +3,7 @@

define i1 @test_umax1(i32 %n) {
; CHECK-LABEL: @test_umax1(
; CHECK-NEXT: [[C1:%.*]] = icmp ugt i32 [[N:%.*]], 10
; CHECK-NEXT: [[S:%.*]] = select i1 [[C1]], i32 [[N]], i32 10
; CHECK-NEXT: [[C2:%.*]] = icmp ugt i32 [[S]], 9
; CHECK-NEXT: ret i1 [[C2]]
; CHECK-NEXT: ret i1 true
;
%c1 = icmp ugt i32 %n, 10
%s = select i1 %c1, i32 %n, i32 10
@@ -40,10 +37,7 @@ define i1 @test_umax3(i32 %n) {

define i1 @test_umin1(i32 %n) {
; CHECK-LABEL: @test_umin1(
; CHECK-NEXT: [[C1:%.*]] = icmp ult i32 [[N:%.*]], 10
; CHECK-NEXT: [[S:%.*]] = select i1 [[C1]], i32 [[N]], i32 10
; CHECK-NEXT: [[C2:%.*]] = icmp ult i32 [[S]], 11
; CHECK-NEXT: ret i1 [[C2]]
; CHECK-NEXT: ret i1 true
;
%c1 = icmp ult i32 %n, 10
%s = select i1 %c1, i32 %n, i32 10
@@ -77,10 +71,7 @@ define i1 @test_umin3(i32 %n) {

define i1 @test_smax1(i32 %n) {
; CHECK-LABEL: @test_smax1(
; CHECK-NEXT: [[C1:%.*]] = icmp sgt i32 [[N:%.*]], -10
; CHECK-NEXT: [[S:%.*]] = select i1 [[C1]], i32 [[N]], i32 -10
; CHECK-NEXT: [[C2:%.*]] = icmp sgt i32 [[S]], -11
; CHECK-NEXT: ret i1 [[C2]]
; CHECK-NEXT: ret i1 true
;
%c1 = icmp sgt i32 %n, -10
%s = select i1 %c1, i32 %n, i32 -10
@@ -114,10 +105,7 @@ define i1 @test_smax3(i32 %n) {

define i1 @test_smin1(i32 %n) {
; CHECK-LABEL: @test_smin1(
; CHECK-NEXT: [[C1:%.*]] = icmp slt i32 [[N:%.*]], 10
; CHECK-NEXT: [[S:%.*]] = select i1 [[C1]], i32 [[N]], i32 10
; CHECK-NEXT: [[C2:%.*]] = icmp slt i32 [[S]], 11
; CHECK-NEXT: ret i1 [[C2]]
; CHECK-NEXT: ret i1 true
;
%c1 = icmp slt i32 %n, 10
%s = select i1 %c1, i32 %n, i32 10

0 comments on commit 106f0cd

Please sign in to comment.