[llvm] r336509 - [LoopIdiomRecognize] Support for converting loops that use LSHR to CTLZ.
Topper, Craig via llvm-commits
llvm-commits at lists.llvm.org
Wed Jul 11 15:02:49 PDT 2018
I should have a fix soon.
This case is also broken independent of the recent patch
unsigned foo(int input) { // signed type
if (input < 0)
input = -input; // absolute value
unsigned num = 0;
do {
++num;
input >>= 1;
} while (input != 0);
return num;
}
int main() {
__builtin_printf("%u\n", foo(0));
}
From: Eric Christopher [mailto:echristo at gmail.com]
Sent: Wednesday, July 11, 2018 2:54 PM
To: Wei Mi <wmi at google.com>
Cc: Topper, Craig <craig.topper at intel.com>; llvm-commits <llvm-commits at lists.llvm.org>
Subject: Re: [llvm] r336509 - [LoopIdiomRecognize] Support for converting loops that use LSHR to CTLZ.
Hi Craig,
Since we have a testcase here, could we get this reverted until we can get a fix (unless you'll have one shortly of course :).
Thanks!
-eric
On Wed, Jul 11, 2018 at 1:43 PM Wei Mi via llvm-commits <llvm-commits at lists.llvm.org<mailto:llvm-commits at lists.llvm.org>> wrote:
Hi,
We run into a SEGV in a testcase. Here is a reproducible. Please take a look.
----------- 1.cc -------------
unsigned foo(unsigned input) {
unsigned num = 0;
do {
++num;
input >>= 1;
} while (input != 0);
return num;
}
int main() {
__builtin_printf("%u\n", foo(0));
}
---------------------------------
~/workarea/llvm-r336508/rbuild/bin/clang -O2 1.cc -o good.out; ./good.out
1
~/workarea/llvm-r336509/rbuild/bin/clang -O2 1.cc -o bad.out; ./bad.out
0
Thanks,
Wei.
On Sat, Jul 7, 2018 at 6:45 PM, Craig Topper via llvm-commits <llvm-commits at lists.llvm.org<mailto:llvm-commits at lists.llvm.org>> wrote:
Author: ctopper
Date: Sat Jul 7 18:45:47 2018
New Revision: 336509
URL: http://llvm.org/viewvc/llvm-project?rev=336509&view=rev
Log:
[LoopIdiomRecognize] Support for converting loops that use LSHR to CTLZ.
In the 'detectCTLZIdiom' function support for loops that use LSHR instruction instead of ASHR has been added.
This supports creating ctlz from the following code.
int lzcnt(int x) {
int count = 0;
while (x > 0) {
count++;
x = x >> 1;
}
return count;
}
Patch by Olga Moldovanova
Differential Revision: https://reviews.llvm.org/D48354
Modified:
llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
llvm/trunk/test/Transforms/LoopIdiom/X86/ctlz.ll
Modified: llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp?rev=336509&r1=336508&r2=336509&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopIdiomRecognize.cpp Sat Jul 7 18:45:47 2018
@@ -188,8 +188,9 @@ private:
PHINode *CntPhi, Value *Var);
bool recognizeAndInsertCTLZ();
void transformLoopToCountable(BasicBlock *PreCondBB, Instruction *CntInst,
- PHINode *CntPhi, Value *Var, const DebugLoc &DL,
- bool ZeroCheck, bool IsCntPhiUsedOutsideLoop);
+ PHINode *CntPhi, Value *Var, Instruction *DefX,
+ const DebugLoc &DL, bool ZeroCheck,
+ bool IsCntPhiUsedOutsideLoop);
/// @}
};
@@ -1316,8 +1317,8 @@ static bool detectCTLZIdiom(Loop *CurLoo
return false;
// step 2: detect instructions corresponding to "x.next = x >> 1"
- // TODO: Support loops that use LShr.
- if (!DefX || DefX->getOpcode() != Instruction::AShr)
+ if (!DefX || (DefX->getOpcode() != Instruction::AShr &&
+ DefX->getOpcode() != Instruction::LShr))
return false;
ConstantInt *Shft = dyn_cast<ConstantInt>(DefX->getOperand(1));
if (!Shft || !Shft->isOne())
@@ -1401,8 +1402,7 @@ bool LoopIdiomRecognize::recognizeAndIns
// Make sure the initial value can't be negative otherwise the ashr in the
// loop might never reach zero which would make the loop infinite.
- // TODO: Support loops that use lshr and wouldn't need this check.
- if (!isKnownNonNegative(InitX, *DL))
+ if (DefX->getOpcode() == Instruction::AShr && !isKnownNonNegative(InitX, *DL))
return false;
// If we check X != 0 before entering the loop we don't need a zero
@@ -1433,8 +1433,9 @@ bool LoopIdiomRecognize::recognizeAndIns
TargetTransformInfo::TCC_Basic)
return false;
- transformLoopToCountable(PH, CntInst, CntPhi, InitX, DefX->getDebugLoc(),
- ZeroCheck, IsCntPhiUsedOutsideLoop);
+ transformLoopToCountable(PH, CntInst, CntPhi, InitX, DefX,
+ DefX->getDebugLoc(), ZeroCheck,
+ IsCntPhiUsedOutsideLoop);
return true;
}
@@ -1547,7 +1548,8 @@ static CallInst *createCTLZIntrinsic(IRB
/// If CntInst and DefX are not used in LOOP_BODY they will be removed.
void LoopIdiomRecognize::transformLoopToCountable(
BasicBlock *Preheader, Instruction *CntInst, PHINode *CntPhi, Value *InitX,
- const DebugLoc &DL, bool ZeroCheck, bool IsCntPhiUsedOutsideLoop) {
+ Instruction *DefX, const DebugLoc &DL, bool ZeroCheck,
+ bool IsCntPhiUsedOutsideLoop) {
BranchInst *PreheaderBr = cast<BranchInst>(Preheader->getTerminator());
// Step 1: Insert the CTLZ instruction at the end of the preheader block
@@ -1558,10 +1560,16 @@ void LoopIdiomRecognize::transformLoopTo
Builder.SetCurrentDebugLocation(DL);
Value *CTLZ, *Count, *CountPrev, *NewCount, *InitXNext;
- if (IsCntPhiUsedOutsideLoop)
- InitXNext = Builder.CreateAShr(InitX,
- ConstantInt::get(InitX->getType(), 1));
- else
+ if (IsCntPhiUsedOutsideLoop) {
+ if (DefX->getOpcode() == Instruction::AShr)
+ InitXNext =
+ Builder.CreateAShr(InitX, ConstantInt::get(InitX->getType(), 1));
+ else if (DefX->getOpcode() == Instruction::LShr)
+ InitXNext =
+ Builder.CreateLShr(InitX, ConstantInt::get(InitX->getType(), 1));
+ else
+ llvm_unreachable("Unexpected opcode!");
+ } else
InitXNext = InitX;
CTLZ = createCTLZIntrinsic(Builder, InitXNext, DL, ZeroCheck);
Count = Builder.CreateSub(
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=336509&r1=336508&r2=336509&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopIdiom/X86/ctlz.ll (original)
+++ llvm/trunk/test/Transforms/LoopIdiom/X86/ctlz.ll Sat Jul 7 18:45:47 2018
@@ -119,6 +119,52 @@ while.end:
; Here it will replace the loop -
; assume builtin is always profitable.
;
+; int ctlz_zero_check_lshr(int n)
+; {
+; int i = 0;
+; while(n) {
+; n >>= 1;
+; i++;
+; }
+; return i;
+; }
+;
+; ALL: entry
+; ALL: %0 = call i32 @llvm.ctlz.i32(i32 %n, i1 true)
+; ALL-NEXT: %1 = sub i32 32, %0
+; ALL: %inc.lcssa = phi i32 [ %1, %while.body ]
+; ALL: %i.0.lcssa = phi i32 [ 0, %entry ], [ %inc.lcssa, %while.end.loopexit ]
+; ALL: ret i32 %i.0.lcssa
+
+; Function Attrs: norecurse nounwind readnone uwtable
+define i32 @ctlz_zero_check_lshr(i32 %n) {
+entry:
+ %tobool4 = icmp eq i32 %n, 0
+ br i1 %tobool4, label %while.end, label %while.body.preheader
+
+while.body.preheader: ; preds = %entry
+ br label %while.body
+
+while.body: ; preds = %while.body.preheader, %while.body
+ %i.06 = phi i32 [ %inc, %while.body ], [ 0, %while.body.preheader ]
+ %n.addr.05 = phi i32 [ %shr, %while.body ], [ %n, %while.body.preheader ]
+ %shr = lshr i32 %n.addr.05, 1
+ %inc = add nsw i32 %i.06, 1
+ %tobool = icmp eq i32 %shr, 0
+ br i1 %tobool, label %while.end.loopexit, label %while.body
+
+while.end.loopexit: ; preds = %while.body
+ br label %while.end
+
+while.end: ; preds = %while.end.loopexit, %entry
+ %i.0.lcssa = phi i32 [ 0, %entry ], [ %inc, %while.end.loopexit ]
+ ret i32 %i.0.lcssa
+}
+
+; Recognize CTLZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
; int ctlz(int n)
; {
; n = n >= 0 ? n : -n;
@@ -161,6 +207,44 @@ while.end:
; Here it will replace the loop -
; assume builtin is always profitable.
;
+; int ctlz_lshr(int n)
+; {
+; int i = 0;
+; while(n >>= 1) {
+; i++;
+; }
+; return i;
+; }
+;
+; ALL: entry
+; ALL: %0 = lshr i32 %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_lshr(i32 %n) {
+entry:
+ br label %while.cond
+
+while.cond: ; preds = %while.cond, %entry
+ %n.addr.0 = phi i32 [ %n, %entry ], [ %shr, %while.cond ]
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %while.cond ]
+ %shr = lshr 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
+}
+
+; Recognize CTLZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
; int ctlz_add(int n, int i0)
; {
; n = n >= 0 ? n : -n;
@@ -204,6 +288,45 @@ while.end:
; Here it will replace the loop -
; assume builtin is always profitable.
;
+; int ctlz_add_lshr(int n, int i0)
+; {
+; int i = i0;
+; while(n >>= 1) {
+; i++;
+; }
+; return i;
+; }
+;
+; ALL: entry
+; ALL: %0 = lshr i32 %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-NEXT: %4 = add i32 %2, %i0
+; ALL: %i.0.lcssa = phi i32 [ %4, %while.cond ]
+; ALL: ret i32 %i.0.lcssa
+;
+; Function Attrs: norecurse nounwind readnone uwtable
+define i32 @ctlz_add_lshr(i32 %n, i32 %i0) {
+entry:
+ br label %while.cond
+
+while.cond: ; preds = %while.cond, %entry
+ %n.addr.0 = phi i32 [ %n, %entry ], [ %shr, %while.cond ]
+ %i.0 = phi i32 [ %i0, %entry ], [ %inc, %while.cond ]
+ %shr = lshr 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
+}
+
+; Recognize CTLZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
; int ctlz_sext(short in)
; {
; int n = in;
@@ -240,6 +363,45 @@ while.cond:
%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
+}
+
+; Recognize CTLZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
+; int ctlz_sext_lshr(short in)
+; {
+; int i = 0;
+; while(in >>= 1) {
+; i++;
+; }
+; return i;
+; }
+;
+; ALL: entry
+; ALL: %0 = lshr i32 %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_lshr(i16 %in) {
+entry:
+ %n = sext i16 %in to i32
+ br label %while.cond
+
+while.cond: ; preds = %while.cond, %entry
+ %n.addr.0 = phi i32 [ %n, %entry ], [ %shr, %while.cond ]
+ %i.0 = phi i32 [ 0, %entry ], [ %inc, %while.cond ]
+ %shr = lshr 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
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