RPCS3/llvm-mirror
1
0
Fork 0
mirror of https://github.com/RPCS3/llvm-mirror.git synced 2024-11-22 18:54:02 +01:00
Code Issues Projects Releases Wiki Activity

[InstCombine] avoid infinite loops with select/icmp transforms

Browse Source 
This fixes https://llvm.org/PR48900 , but as seen in the
regression tests prevents some optimizations.

There are a few options to restore those (switch to min/max
intrinsics, add larger pattern matching for select with
dominating condition, improve CVP), but we need to prevent
the bug 1st.
This commit is contained in:
Sanjay Patel 2021-05-04 11:43:01 -04:00
parent 506fd61a96
commit 30e39a65e1
2 changed files with 79 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1500,6 +1500,12 @@ Instruction *InstCombinerImpl::foldICmpWithDominatingICmp(ICmpInst &Cmp) {
if (Cmp.isEquality() || (IsSignBit && hasBranchUse(Cmp)))
return nullptr;
// Avoid an infinite loop with min/max canonicalization.
// TODO: This will be unnecessary if we canonicalize to min/max intrinsics.
if (Cmp.hasOneUse() &&
match(Cmp.user_back(), m_MaxOrMin(m_Value(), m_Value())))
return nullptr;
if (const APInt *EqC = Intersection.getSingleElement())
return new ICmpInst(ICmpInst::ICMP_EQ, X, Builder.getInt(*EqC));
if (const APInt *NeC = Difference.getSingleElement())

77
test/Transforms/InstCombine/icmp-dom.ll
View File

@ -67,6 +67,9 @@ lor.end:
ret void
}
; TODO: cmp3 could be reduced to A != B, but we miss that
; while avoiding an infinite loop with min/max canonicalization.
define void @idom_sign_bit_check_edge_dominates_select(i64 %a, i64 %b) {
; CHECK-LABEL: @idom_sign_bit_check_edge_dominates_select(
; CHECK-NEXT: entry:
@ -75,8 +78,10 @@ define void @idom_sign_bit_check_edge_dominates_select(i64 %a, i64 %b) {
; CHECK: land.lhs.true:
; CHECK-NEXT: br label [[LOR_END:%.*]]
; CHECK: lor.rhs:
; CHECK-NEXT: [[CMP3:%.*]] = icmp eq i64 [[A]], [[B:%.*]]
; CHECK-NEXT: br i1 [[CMP3]], label [[LOR_END]], label [[LAND_RHS:%.*]]
; CHECK-NEXT: [[CMP2:%.*]] = icmp sgt i64 [[A]], 5
; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[CMP2]], i64 [[A]], i64 5
; CHECK-NEXT: [[CMP3_NOT:%.*]] = icmp eq i64 [[SELECT]], [[B:%.*]]
; CHECK-NEXT: br i1 [[CMP3_NOT]], label [[LOR_END]], label [[LAND_RHS:%.*]]
; CHECK: land.rhs:
; CHECK-NEXT: br label [[LOR_END]]
; CHECK: lor.end:
@ -130,14 +135,19 @@ lor.end:
ret void
}
; TODO: cmp2 could be reduced to A != B, but we miss that
; while avoiding an infinite loop with min/max canonicalization.
define void @idom_not_zbranch(i32 %a, i32 %b) {
; CHECK-LABEL: @idom_not_zbranch(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i32 [[A:%.*]], 0
; CHECK-NEXT: br i1 [[CMP]], label [[RETURN:%.*]], label [[IF_END:%.*]]
; CHECK: if.end:
; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i32 [[A]], [[B:%.*]]
; CHECK-NEXT: br i1 [[CMP2]], label [[RETURN]], label [[IF_THEN3:%.*]]
; CHECK-NEXT: [[CMP1:%.*]] = icmp slt i32 [[A]], 0
; CHECK-NEXT: [[A_:%.*]] = select i1 [[CMP1]], i32 [[A]], i32 0
; CHECK-NEXT: [[CMP2_NOT:%.*]] = icmp eq i32 [[A_]], [[B:%.*]]
; CHECK-NEXT: br i1 [[CMP2_NOT]], label [[RETURN]], label [[IF_THEN3:%.*]]
; CHECK: if.then3:
; CHECK-NEXT: br label [[RETURN]]
; CHECK: return:
@ -348,3 +358,62 @@ f:
ret i1 %cmp2
}
; This used to infinite loop because of a conflict
; with min/max canonicalization.
define i32 @PR48900(i32 %i, i1* %p) {
; CHECK-LABEL: @PR48900(
; CHECK-NEXT: [[MAXCMP:%.*]] = icmp ugt i32 [[I:%.*]], 1
; CHECK-NEXT: [[UMAX:%.*]] = select i1 [[MAXCMP]], i32 [[I]], i32 1
; CHECK-NEXT: [[I4:%.*]] = icmp sgt i32 [[UMAX]], 0
; CHECK-NEXT: br i1 [[I4]], label [[TRUELABEL:%.*]], label [[FALSELABEL:%.*]]
; CHECK: truelabel:
; CHECK-NEXT: [[MINCMP:%.*]] = icmp ult i32 [[UMAX]], 2
; CHECK-NEXT: [[SMIN:%.*]] = select i1 [[MINCMP]], i32 [[UMAX]], i32 2
; CHECK-NEXT: ret i32 [[SMIN]]
; CHECK: falselabel:
; CHECK-NEXT: ret i32 0
;
%maxcmp = icmp ugt i32 %i, 1
%umax = select i1 %maxcmp, i32 %i, i32 1
%i4 = icmp sgt i32 %umax, 0
br i1 %i4, label %truelabel, label %falselabel
truelabel:
%mincmp = icmp ult i32 %umax, 2
%smin = select i1 %mincmp, i32 %umax, i32 2
ret i32 %smin
falselabel:
ret i32 0
}
; This used to infinite loop because of a conflict
; with min/max canonicalization.
define i8 @PR48900_alt(i8 %i, i1* %p) {
; CHECK-LABEL: @PR48900_alt(
; CHECK-NEXT: [[MAXCMP:%.*]] = icmp sgt i8 [[I:%.*]], -127
; CHECK-NEXT: [[SMAX:%.*]] = select i1 [[MAXCMP]], i8 [[I]], i8 -127
; CHECK-NEXT: [[I4:%.*]] = icmp ugt i8 [[SMAX]], -128
; CHECK-NEXT: br i1 [[I4]], label [[TRUELABEL:%.*]], label [[FALSELABEL:%.*]]
; CHECK: truelabel:
; CHECK-NEXT: [[MINCMP:%.*]] = icmp slt i8 [[SMAX]], -126
; CHECK-NEXT: [[UMIN:%.*]] = select i1 [[MINCMP]], i8 [[SMAX]], i8 -126
; CHECK-NEXT: ret i8 [[UMIN]]
; CHECK: falselabel:
; CHECK-NEXT: ret i8 0
;
%maxcmp = icmp sgt i8 %i, -127
%smax = select i1 %maxcmp, i8 %i, i8 -127
%i4 = icmp ugt i8 %smax, 128
br i1 %i4, label %truelabel, label %falselabel
truelabel:
%mincmp = icmp slt i8 %smax, -126
%umin = select i1 %mincmp, i8 %smax, i8 -126
ret i8 %umin
falselabel:
ret i8 0
}