[polly] r238905 - Translate power-of-two floor-division into ashr
David Majnemer
david.majnemer at gmail.com
Wed Jun 3 00:58:38 PDT 2015
On Tue, Jun 2, 2015 at 11:31 PM, Tobias Grosser <tobias at grosser.es> wrote:
> Author: grosser
> Date: Wed Jun 3 01:31:30 2015
> New Revision: 238905
>
> URL: http://llvm.org/viewvc/llvm-project?rev=238905&view=rev
> Log:
> Translate power-of-two floor-division into ashr
>
> Power-of-two floor divisions can be translated into an arithmetic shift
> operation. This allows us to replace a complex lowering that requires
> division
> operations:
>
This only holds if the numerator is non-negative. -1/INT_MIN should give 0
but calculating it with a right-shift would give -1.
>
> %pexp.fdiv_q.0 = sub i64 %21, 128
> %pexp.fdiv_q.1 = add i64 %pexp.fdiv_q.0, 1
> %pexp.fdiv_q.2 = icmp slt i64 %21, 0
> %pexp.fdiv_q.3 = select i1 %pexp.fdiv_q.2, i64 %pexp.fdiv_q.1, i64 %21
> %pexp.fdiv_q.4 = sdiv i64 %pexp.fdiv_q.3, 128
>
> with a simple ashr:
>
> %polly.fdiv_q.shr = ashr i64 %21, 7
>
> Added:
>
> polly/trunk/test/Isl/CodeGen/exprModDiv___%for.cond---%for.end.jscop.pow2
> - copied, changed from r238645,
> polly/trunk/test/Isl/CodeGen/exprModDiv___%for.cond---%for.end.jscop
> Modified:
> polly/trunk/lib/CodeGen/IslExprBuilder.cpp
> polly/trunk/test/Isl/CodeGen/exprModDiv.ll
> polly/trunk/test/Isl/CodeGen/exprModDiv___%for.cond---%for.end.jscop
>
> Modified: polly/trunk/lib/CodeGen/IslExprBuilder.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/polly/trunk/lib/CodeGen/IslExprBuilder.cpp?rev=238905&r1=238904&r2=238905&view=diff
>
> ==============================================================================
> --- polly/trunk/lib/CodeGen/IslExprBuilder.cpp (original)
> +++ polly/trunk/lib/CodeGen/IslExprBuilder.cpp Wed Jun 3 01:31:30 2015
> @@ -301,6 +301,11 @@ Value *IslExprBuilder::createOpBin(__isl
> Res = Builder.CreateUDiv(LHS, RHS, "pexp.p_div_q");
> break;
> case isl_ast_op_fdiv_q: { // Round towards -infty
> + auto &Int = dyn_cast<ConstantInt>(RHS)->getValue();
>
The dyn_cast seems superfluous if you immediately dereference it. If the
dyn_cast cannot fail, please use cast.
> + if (Int.isPowerOf2()) {
> + Res = Builder.CreateAShr(LHS, Int.ceilLogBase2(),
> "polly.fdiv_q.shr");
> + break;
> + }
> // TODO: Review code and check that this calculation does not yield
> // incorrect overflow in some bordercases.
> //
>
> Modified: polly/trunk/test/Isl/CodeGen/exprModDiv.ll
> URL:
> http://llvm.org/viewvc/llvm-project/polly/trunk/test/Isl/CodeGen/exprModDiv.ll?rev=238905&r1=238904&r2=238905&view=diff
>
> ==============================================================================
> --- polly/trunk/test/Isl/CodeGen/exprModDiv.ll (original)
> +++ polly/trunk/test/Isl/CodeGen/exprModDiv.ll Wed Jun 3 01:31:30 2015
> @@ -1,4 +1,5 @@
> ; RUN: opt %loadPolly -polly-import-jscop -polly-import-jscop-dir=%S
> -polly-codegen -S < %s | FileCheck %s
> +; RUN: opt %loadPolly -polly-import-jscop -polly-import-jscop-dir=%S
> -polly-codegen -polly-import-jscop-postfix=pow2 -S < %s | FileCheck %s
> -check-prefix=POW2
> ;
> ; void exprModDiv(float *A, float *B, float *C, long N, long p) {
> ; for (long i = 0; i < N; i++)
> @@ -12,34 +13,58 @@
> ; useful as LLVM will translate urem and udiv operations with power-of-two
> ; denominators to fast bitwise and or shift operations.
>
> -; A[i % 128]
> -; CHECK: %pexp.pdiv_r = urem i64 %polly.indvar, 128
> +; A[i % 127]
> +; CHECK: %pexp.pdiv_r = urem i64 %polly.indvar, 127
> ; CHECK: %polly.access.A6 = getelementptr float, float* %A, i64
> %pexp.pdiv_r
>
> -; A[i / 128]
> -; CHECK: %pexp.div = sdiv i64 %polly.indvar, 128
> +; A[i / 127]
> +; CHECK: %pexp.div = sdiv i64 %polly.indvar, 127
> ; CHECK: %polly.access.B8 = getelementptr float, float* %B, i64 %pexp.div
> ;
> ; FIXME: Make isl mark this as an udiv expression.
>
> ; #define floord(n,d) ((n < 0) ? (n - d + 1) : n) / d
> -; A[p + 128 * floord(-p - 1, 128) + 128]
> +; A[p + 127 * floord(-p - 1, 127) + 127]
> ; CHECK: %20 = sub nsw i64 0, %p
> ; CHECK: %21 = sub nsw i64 %20, 1
> -; CHECK: %pexp.fdiv_q.0 = sub i64 %21, 128
> +; CHECK: %pexp.fdiv_q.0 = sub i64 %21, 127
> ; CHECK: %pexp.fdiv_q.1 = add i64 %pexp.fdiv_q.0, 1
> ; CHECK: %pexp.fdiv_q.2 = icmp slt i64 %21, 0
> ; CHECK: %pexp.fdiv_q.3 = select i1 %pexp.fdiv_q.2, i64 %pexp.fdiv_q.1,
> i64 %21
> -; CHECK: %pexp.fdiv_q.4 = sdiv i64 %pexp.fdiv_q.3, 128
> -; CHECK: %22 = mul nsw i64 128, %pexp.fdiv_q.4
> +; CHECK: %pexp.fdiv_q.4 = sdiv i64 %pexp.fdiv_q.3, 127
> +; CHECK: %22 = mul nsw i64 127, %pexp.fdiv_q.4
> ; CHECK: %23 = add nsw i64 %p, %22
> -; CHECK: %24 = add nsw i64 %23, 128
> +; CHECK: %24 = add nsw i64 %23, 127
> ; CHECK: %polly.access.A10 = getelementptr float, float* %A, i64 %24
>
> -; A[p / 128]
> -; CHECK: %pexp.div12 = sdiv i64 %p, 128
> +; A[p / 127]
> +; CHECK: %pexp.div12 = sdiv i64 %p, 127
> ; CHECK: %polly.access.B13 = getelementptr float, float* %B, i64
> %pexp.div12
>
> +; A[i % 128]
> +; POW2: %pexp.pdiv_r = urem i64 %polly.indvar, 128
> +; POW2: %polly.access.A6 = getelementptr float, float* %A, i64
> %pexp.pdiv_r
> +
> +; A[i / 128]
> +; POW2: %pexp.div = sdiv i64 %polly.indvar, 128
> +; POW2: %polly.access.B8 = getelementptr float, float* %B, i64 %pexp.div
> +;
> +; FIXME: Make isl mark this as an udiv expression.
> +
> +; #define floord(n,d) ((n < 0) ? (n - d + 1) : n) / d
> +; A[p + 128 * floord(-p - 1, 128) + 128]
> +; POW2: %20 = sub nsw i64 0, %p
> +; POW2: %21 = sub nsw i64 %20, 1
> +; POW2: %polly.fdiv_q.shr = ashr i64 %21, 7
> +; POW2: %22 = mul nsw i64 128, %polly.fdiv_q.shr
> +; POW2: %23 = add nsw i64 %p, %22
> +; POW2: %24 = add nsw i64 %23, 128
> +; POW2: %polly.access.A10 = getelementptr float, float* %A, i64 %24
> +
> +; A[p / 128]
> +; POW2: %pexp.div12 = sdiv i64 %p, 128
> +; POW2: %polly.access.B13 = getelementptr float, float* %B, i64
> %pexp.div12
> +
> target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
>
> define void @exprModDiv(float* %A, float* %B, float* %C, i64 %N, i64 %p) {
>
> Modified:
> polly/trunk/test/Isl/CodeGen/exprModDiv___%for.cond---%for.end.jscop
> URL:
> http://llvm.org/viewvc/llvm-project/polly/trunk/test/Isl/CodeGen/exprModDiv___%25for.cond---%25for.end.jscop?rev=238905&r1=238904&r2=238905&view=diff
>
> ==============================================================================
> --- polly/trunk/test/Isl/CodeGen/exprModDiv___%for.cond---%for.end.jscop
> (original)
> +++ polly/trunk/test/Isl/CodeGen/exprModDiv___%for.cond---%for.end.jscop
> Wed Jun 3 01:31:30 2015
> @@ -6,19 +6,19 @@
> "accesses" : [
> {
> "kind" : "read",
> - "relation" : "[N, p] -> { Stmt_for_body[i0] -> MemRef_A[i0
> % 128] }"
> + "relation" : "[N, p] -> { Stmt_for_body[i0] -> MemRef_A[i0
> % 127] }"
> },
> {
> "kind" : "read",
> - "relation" : "[N, p] -> { Stmt_for_body[i0] -> MemRef_B[i0
> / 128] }"
> + "relation" : "[N, p] -> { Stmt_for_body[i0] -> MemRef_B[i0
> / 127] }"
> },
> {
> "kind" : "read",
> - "relation" : "[N, p] -> { Stmt_for_body[i0] -> MemRef_A[p
> % 128] }"
> + "relation" : "[N, p] -> { Stmt_for_body[i0] -> MemRef_A[p
> % 127] }"
> },
> {
> "kind" : "read",
> - "relation" : "[N, p] -> { Stmt_for_body[i0] -> MemRef_B[p
> / 128] }"
> + "relation" : "[N, p] -> { Stmt_for_body[i0] -> MemRef_B[p
> / 127] }"
> },
> {
> "kind" : "read",
>
> Copied:
> polly/trunk/test/Isl/CodeGen/exprModDiv___%for.cond---%for.end.jscop.pow2
> (from r238645,
> polly/trunk/test/Isl/CodeGen/exprModDiv___%for.cond---%for.end.jscop)
> URL:
> http://llvm.org/viewvc/llvm-project/polly/trunk/test/Isl/CodeGen/exprModDiv___%25for.cond---%25for.end.jscop.pow2?p2=polly/trunk/test/Isl/CodeGen/exprModDiv___%25for.cond---%25for.end.jscop.pow2&p1=polly/trunk/test/Isl/CodeGen/exprModDiv___%25for.cond---%25for.end.jscop&r1=238645&r2=238905&rev=238905&view=diff
>
> ==============================================================================
> (empty)
>
>
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