[llvm] r220960 - [SCEV] Improve Scalar Evolution's use of no {un, }signed wrap flags
Philip Reames
listmail at philipreames.com
Fri Oct 31 11:50:30 PDT 2014
On 10/31/2014 04:40 AM, Bradley Smith wrote:
> Author: brasmi01
> Date: Fri Oct 31 06:40:32 2014
> New Revision: 220960
>
> URL: http://llvm.org/viewvc/llvm-project?rev=220960&view=rev
> Log:
> [SCEV] Improve Scalar Evolution's use of no {un,}signed wrap flags
>
> In a case where we have a no {un,}signed wrap flag on the increment, if
> RHS - Start is constant then we can avoid inserting a max operation bewteen
> the two, since we can statically determine which is greater.
>
> This allows us to unroll loops such as:
>
> void testcase3(int v) {
> for (int i=v; i<=v+1; ++i)
> f(i);
> }
>
> Added:
> llvm/trunk/test/Transforms/LoopUnroll/nsw-tripcount.ll
> Modified:
> llvm/trunk/lib/Analysis/ScalarEvolution.cpp
> llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll
>
> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=220960&r1=220959&r2=220960&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Fri Oct 31 06:40:32 2014
> @@ -6964,9 +6964,19 @@ ScalarEvolution::HowManyLessThans(const
> : ICmpInst::ICMP_ULT;
> const SCEV *Start = IV->getStart();
> const SCEV *End = RHS;
> - if (!isLoopEntryGuardedByCond(L, Cond, getMinusSCEV(Start, Stride), RHS))
> - End = IsSigned ? getSMaxExpr(RHS, Start)
> - : getUMaxExpr(RHS, Start);
> + if (!isLoopEntryGuardedByCond(L, Cond, getMinusSCEV(Start, Stride), RHS)) {
> + const SCEV *Diff = getMinusSCEV(RHS, Start);
> + // If we have NoWrap set, then we can assume that the increment won't
> + // overflow, in which case if RHS - Start is a constant, we don't need to
> + // do a max operation since we can just figure it out statically
> + if (NoWrap && isa<SCEVConstant>(Diff)) {
> + APInt D = dyn_cast<const SCEVConstant>(Diff)->getValue()->getValue();
This dyn_cast should be a cast
> + if (D.isNegative())
> + End = Start;
> + } else
> + End = IsSigned ? getSMaxExpr(RHS, Start)
> + : getUMaxExpr(RHS, Start);
> + }
>
> const SCEV *BECount = computeBECount(getMinusSCEV(End, Start), Stride, false);
>
> @@ -7035,9 +7045,19 @@ ScalarEvolution::HowManyGreaterThans(con
>
> const SCEV *Start = IV->getStart();
> const SCEV *End = RHS;
> - if (!isLoopEntryGuardedByCond(L, Cond, getAddExpr(Start, Stride), RHS))
> - End = IsSigned ? getSMinExpr(RHS, Start)
> - : getUMinExpr(RHS, Start);
> + if (!isLoopEntryGuardedByCond(L, Cond, getAddExpr(Start, Stride), RHS)) {
> + const SCEV *Diff = getMinusSCEV(RHS, Start);
> + // If we have NoWrap set, then we can assume that the increment won't
> + // overflow, in which case if RHS - Start is a constant, we don't need to
> + // do a max operation since we can just figure it out statically
> + if (NoWrap && isa<SCEVConstant>(Diff)) {
> + APInt D = dyn_cast<const SCEVConstant>(Diff)->getValue()->getValue();
Same here
> + if (!D.isNegative())
> + End = Start;
> + } else
> + End = IsSigned ? getSMinExpr(RHS, Start)
> + : getUMinExpr(RHS, Start);
> + }
>
> const SCEV *BECount = computeBECount(getMinusSCEV(Start, End), Stride, false);
>
>
> Modified: llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll?rev=220960&r1=220959&r2=220960&view=diff
> ==============================================================================
> --- llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll (original)
> +++ llvm/trunk/test/Analysis/ScalarEvolution/nsw.ll Fri Oct 31 06:40:32 2014
> @@ -123,9 +123,8 @@ exit:
> ret i32 %result
> }
>
> -; TODO: This could fold down to '1'
> ; CHECK-LABEL: PR12375
> -; CHECK: --> {(4 + %arg),+,4}<nuw><%bb1> Exits: (4 + (4 * ((-1 + (-1 * %arg) + ((4 + %arg) umax (8 + %arg)<nsw>)) /u 4)) + %arg)
> +; CHECK: --> {(4 + %arg),+,4}<nuw><%bb1> Exits: (8 + %arg)<nsw>
> define i32 @PR12375(i32* readnone %arg) {
> bb:
> %tmp = getelementptr inbounds i32* %arg, i64 2
> @@ -158,3 +157,23 @@ bb2:
> bb5: ; preds = %bb2
> ret void
> }
> +
> +declare void @f(i32)
> +
> +; CHECK-LABEL: nswnowrap
> +; CHECK: --> {(1 + %v),+,1}<nsw><%for.body> Exits: (2 + %v)
> +define void @nswnowrap(i32 %v) {
> +entry:
> + %add = add nsw i32 %v, 1
> + br label %for.body
> +
> +for.body:
> + %i.04 = phi i32 [ %v, %entry ], [ %inc, %for.body ]
> + %inc = add nsw i32 %i.04, 1
> + tail call void @f(i32 %i.04)
> + %cmp = icmp slt i32 %i.04, %add
> + br i1 %cmp, label %for.body, label %for.end
> +
> +for.end:
> + ret void
> +}
>
> Added: llvm/trunk/test/Transforms/LoopUnroll/nsw-tripcount.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/nsw-tripcount.ll?rev=220960&view=auto
> ==============================================================================
> --- llvm/trunk/test/Transforms/LoopUnroll/nsw-tripcount.ll (added)
> +++ llvm/trunk/test/Transforms/LoopUnroll/nsw-tripcount.ll Fri Oct 31 06:40:32 2014
> @@ -0,0 +1,32 @@
> +; RUN: opt -loop-unroll -S %s | FileCheck %s
> +
> +; extern void f(int);
> +; void test1(int v) {
> +; for (int i=v; i<=v+1; ++i)
> +; f(i);
> +; }
> +;
> +; We can use the nsw information to see that the tripcount will be 2, so the
> +; loop should be unrolled as this is always beneficial
> +
> +declare void @f(i32)
> +
> +; CHECK-LABEL: @test1
> +define void @test1(i32 %v) {
> +entry:
> + %add = add nsw i32 %v, 1
> + br label %for.body
> +
> +for.body:
> + %i.04 = phi i32 [ %v, %entry ], [ %inc, %for.body ]
> + tail call void @f(i32 %i.04)
> + %inc = add nsw i32 %i.04, 1
> + %cmp = icmp slt i32 %i.04, %add
> + br i1 %cmp, label %for.body, label %for.end
> +
> +; CHECK: call void @f
> +; CHECK-NOT: br i1
> +; CHECK: call void @f
> +for.end:
> + ret void
> +}
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
More information about the llvm-commits
mailing list