[llvm] r333927 - [ValueTracking] Match select abs pattern when there's an sext involved
John Brawn via llvm-commits
llvm-commits at lists.llvm.org
Mon Jun 4 09:53:57 PDT 2018
Author: john.brawn
Date: Mon Jun 4 09:53:57 2018
New Revision: 333927
URL: http://llvm.org/viewvc/llvm-project?rev=333927&view=rev
Log:
[ValueTracking] Match select abs pattern when there's an sext involved
When checking a select to see if it matches an abs, allow the true/false values
to be a sign-extension of the comparison value instead of requiring that they're
directly the comparison value, as all the comparison cares about is the sign of
the value.
This fixes a regression due to r333702, where we were no longer generating ctlz
due to isKnownNonNegative failing to match such a pattern.
Differential Revision: https://reviews.llvm.org/D47631
Modified:
llvm/trunk/lib/Analysis/ValueTracking.cpp
llvm/trunk/test/Transforms/LoopIdiom/ARM/ctlz.ll
llvm/trunk/test/Transforms/LoopIdiom/X86/ctlz.ll
Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=333927&r1=333926&r2=333927&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Mon Jun 4 09:53:57 2018
@@ -4604,23 +4604,35 @@ static SelectPatternResult matchSelectPa
const APInt *C1;
if (match(CmpRHS, m_APInt(C1))) {
- if ((CmpLHS == TrueVal && match(FalseVal, m_Neg(m_Specific(CmpLHS)))) ||
- (CmpLHS == FalseVal && match(TrueVal, m_Neg(m_Specific(CmpLHS))))) {
- // Set RHS to the negate operand. LHS was assigned to CmpLHS earlier.
- RHS = (CmpLHS == TrueVal) ? FalseVal : TrueVal;
+ // Sign-extending LHS does not change its sign, so TrueVal/FalseVal can
+ // match against either LHS or sext(LHS).
+ auto MaybeSExtLHS = m_CombineOr(m_Specific(CmpLHS),
+ m_SExt(m_Specific(CmpLHS)));
+ if ((match(TrueVal, MaybeSExtLHS) &&
+ match(FalseVal, m_Neg(m_Specific(TrueVal)))) ||
+ (match(FalseVal, MaybeSExtLHS) &&
+ match(TrueVal, m_Neg(m_Specific(FalseVal))))) {
+ // Set LHS and RHS so that RHS is the negated operand of the select
+ if (match(TrueVal, MaybeSExtLHS)) {
+ LHS = TrueVal;
+ RHS = FalseVal;
+ } else {
+ LHS = FalseVal;
+ RHS = TrueVal;
+ }
// ABS(X) ==> (X >s 0) ? X : -X and (X >s -1) ? X : -X
// NABS(X) ==> (X >s 0) ? -X : X and (X >s -1) ? -X : X
if (Pred == ICmpInst::ICMP_SGT &&
(C1->isNullValue() || C1->isAllOnesValue())) {
- return {(CmpLHS == TrueVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false};
+ return {(LHS == TrueVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false};
}
// ABS(X) ==> (X <s 0) ? -X : X and (X <s 1) ? -X : X
// NABS(X) ==> (X <s 0) ? X : -X and (X <s 1) ? X : -X
if (Pred == ICmpInst::ICMP_SLT &&
(C1->isNullValue() || C1->isOneValue())) {
- return {(CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false};
+ return {(LHS == FalseVal) ? SPF_ABS : SPF_NABS, SPNB_NA, false};
}
}
}
Modified: llvm/trunk/test/Transforms/LoopIdiom/ARM/ctlz.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopIdiom/ARM/ctlz.ll?rev=333927&r1=333926&r2=333927&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopIdiom/ARM/ctlz.ll (original)
+++ llvm/trunk/test/Transforms/LoopIdiom/ARM/ctlz.ll Mon Jun 4 09:53:57 2018
@@ -199,3 +199,48 @@ while.cond:
while.end: ; preds = %while.cond
ret i32 %i.0
}
+
+; Recognize CTLZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
+; int ctlz_sext(short in)
+; {
+; int n = in;
+; if (in < 0)
+; n = -n;
+; int i = 0;
+; while(n >>= 1) {
+; i++;
+; }
+; return i;
+; }
+;
+; ALL: entry
+; ALL: %0 = ashr i32 %abs_n, 1
+; ALL-NEXT: %1 = call i32 @llvm.ctlz.i32(i32 %0, i1 false)
+; ALL-NEXT: %2 = sub i32 32, %1
+; ALL-NEXT: %3 = add i32 %2, 1
+; ALL: %i.0.lcssa = phi i32 [ %2, %while.cond ]
+; ALL: ret i32 %i.0.lcssa
+
+; Function Attrs: norecurse nounwind readnone uwtable
+define i32 @ctlz_sext(i16 %in) {
+entry:
+ %n = sext i16 %in to i32
+ %c = icmp sgt i16 %in, 0
+ %negn = sub nsw i32 0, %n
+ %abs_n = select i1 %c, i32 %n, i32 %negn
+ br label %while.cond
+
+while.cond: ; preds = %while.cond, %entry
+ %n.addr.0 = phi i32 [ %abs_n, %entry ], [ %shr, %while.cond ]
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %while.cond ]
+ %shr = ashr i32 %n.addr.0, 1
+ %tobool = icmp eq i32 %shr, 0
+ %inc = add nsw i32 %i.0, 1
+ br i1 %tobool, label %while.end, label %while.cond
+
+while.end: ; preds = %while.cond
+ ret i32 %i.0
+}
Modified: llvm/trunk/test/Transforms/LoopIdiom/X86/ctlz.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopIdiom/X86/ctlz.ll?rev=333927&r1=333926&r2=333927&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopIdiom/X86/ctlz.ll (original)
+++ llvm/trunk/test/Transforms/LoopIdiom/X86/ctlz.ll Mon Jun 4 09:53:57 2018
@@ -200,6 +200,51 @@ while.end:
ret i32 %i.0
}
+; Recognize CTLZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
+; int ctlz_sext(short in)
+; {
+; int n = in;
+; if (in < 0)
+; n = -n;
+; int i = 0;
+; while(n >>= 1) {
+; i++;
+; }
+; return i;
+; }
+;
+; ALL: entry
+; ALL: %0 = ashr i32 %abs_n, 1
+; ALL-NEXT: %1 = call i32 @llvm.ctlz.i32(i32 %0, i1 false)
+; ALL-NEXT: %2 = sub i32 32, %1
+; ALL-NEXT: %3 = add i32 %2, 1
+; ALL: %i.0.lcssa = phi i32 [ %2, %while.cond ]
+; ALL: ret i32 %i.0.lcssa
+
+; Function Attrs: norecurse nounwind readnone uwtable
+define i32 @ctlz_sext(i16 %in) {
+entry:
+ %n = sext i16 %in to i32
+ %c = icmp sgt i16 %in, 0
+ %negn = sub nsw i32 0, %n
+ %abs_n = select i1 %c, i32 %n, i32 %negn
+ br label %while.cond
+
+while.cond: ; preds = %while.cond, %entry
+ %n.addr.0 = phi i32 [ %abs_n, %entry ], [ %shr, %while.cond ]
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %while.cond ]
+ %shr = ashr i32 %n.addr.0, 1
+ %tobool = icmp eq i32 %shr, 0
+ %inc = add nsw i32 %i.0, 1
+ br i1 %tobool, label %while.end, label %while.cond
+
+while.end: ; preds = %while.cond
+ ret i32 %i.0
+}
+
; This loop contains a volatile store. If x is initially negative,
; the code will be an infinite loop because the ashr will eventually produce
; all ones and continue doing so. This prevents the loop from terminating. If
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