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https://github.com/c64scene-ar/llvm-6502.git
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2918efd551
Summary:
Straight-line strength reduction (SLSR) is implemented in GCC but not yet in
LLVM. It has proven to effectively simplify statements derived from an unrolled
loop, and can potentially benefit many other cases too. For example,
LLVM unrolls
#pragma unroll
foo (int i = 0; i < 3; ++i) {
sum += foo((b + i) * s);
}
into
sum += foo(b * s);
sum += foo((b + 1) * s);
sum += foo((b + 2) * s);
However, no optimizations yet reduce the internal redundancy of the three
expressions:
b * s
(b + 1) * s
(b + 2) * s
With SLSR, LLVM can optimize these three expressions into:
t1 = b * s
t2 = t1 + s
t3 = t2 + s
This commit is only an initial step towards implementing a series of such
optimizations. I will implement more (see TODO in the file commentary) in the
near future. This optimization is enabled for the NVPTX backend for now.
However, I am more than happy to push it to the standard optimization pipeline
after more thorough performance tests.
Test Plan: test/StraightLineStrengthReduce/slsr.ll
Reviewers: eliben, HaoLiu, meheff, hfinkel, jholewinski, atrick
Reviewed By: jholewinski, atrick
Subscribers: karthikthecool, jholewinski, llvm-commits
Differential Revision: http://reviews.llvm.org/D7310
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228016 91177308-0d34-0410-b5e6-96231b3b80d8
120 lines
2.5 KiB
LLVM
120 lines
2.5 KiB
LLVM
; RUN: opt < %s -slsr -gvn -dce -S | FileCheck %s
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declare i32 @foo(i32 %a)
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define i32 @slsr1(i32 %b, i32 %s) {
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; CHECK-LABEL: @slsr1(
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; v0 = foo(b * s);
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%mul0 = mul i32 %b, %s
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; CHECK: mul i32
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; CHECK-NOT: mul i32
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%v0 = call i32 @foo(i32 %mul0)
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; v1 = foo((b + 1) * s);
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%b1 = add i32 %b, 1
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%mul1 = mul i32 %b1, %s
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%v1 = call i32 @foo(i32 %mul1)
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; v2 = foo((b + 2) * s);
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%b2 = add i32 %b, 2
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%mul2 = mul i32 %b2, %s
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%v2 = call i32 @foo(i32 %mul2)
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; return v0 + v1 + v2;
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%1 = add i32 %v0, %v1
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%2 = add i32 %1, %v2
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ret i32 %2
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}
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; v0 = foo(a * b)
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; v1 = foo((a + 1) * b)
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; v2 = foo(a * (b + 1))
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; v3 = foo((a + 1) * (b + 1))
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define i32 @slsr2(i32 %a, i32 %b) {
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; CHECK-LABEL: @slsr2(
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%a1 = add i32 %a, 1
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%b1 = add i32 %b, 1
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%mul0 = mul i32 %a, %b
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; CHECK: mul i32
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; CHECK-NOT: mul i32
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%mul1 = mul i32 %a1, %b
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%mul2 = mul i32 %a, %b1
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%mul3 = mul i32 %a1, %b1
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%v0 = call i32 @foo(i32 %mul0)
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%v1 = call i32 @foo(i32 %mul1)
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%v2 = call i32 @foo(i32 %mul2)
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%v3 = call i32 @foo(i32 %mul3)
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%1 = add i32 %v0, %v1
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%2 = add i32 %1, %v2
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%3 = add i32 %2, %v3
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ret i32 %3
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}
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; The bump is a multiple of the stride.
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;
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; v0 = foo(b * s);
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; v1 = foo((b + 2) * s);
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; v2 = foo((b + 4) * s);
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; return v0 + v1 + v2;
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;
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; ==>
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;
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; mul0 = b * s;
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; v0 = foo(mul0);
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; bump = s * 2;
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; mul1 = mul0 + bump; // GVN ensures mul1 and mul2 use the same bump.
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; v1 = foo(mul1);
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; mul2 = mul1 + bump;
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; v2 = foo(mul2);
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; return v0 + v1 + v2;
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define i32 @slsr3(i32 %b, i32 %s) {
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; CHECK-LABEL: @slsr3(
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%mul0 = mul i32 %b, %s
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; CHECK: mul i32
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%v0 = call i32 @foo(i32 %mul0)
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%b1 = add i32 %b, 2
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%mul1 = mul i32 %b1, %s
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; CHECK: [[BUMP:%[a-zA-Z0-9]+]] = mul i32 %s, 2
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; CHECK: %mul1 = add i32 %mul0, [[BUMP]]
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%v1 = call i32 @foo(i32 %mul1)
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%b2 = add i32 %b, 4
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%mul2 = mul i32 %b2, %s
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; CHECK: %mul2 = add i32 %mul1, [[BUMP]]
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%v2 = call i32 @foo(i32 %mul2)
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%1 = add i32 %v0, %v1
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%2 = add i32 %1, %v2
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ret i32 %2
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}
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; Do not rewrite a candidate if its potential basis does not dominate it.
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; v0 = 0;
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; if (cond)
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; v0 = foo(a * b);
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; v1 = foo((a + 1) * b);
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; return v0 + v1;
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define i32 @not_dominate(i1 %cond, i32 %a, i32 %b) {
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; CHECK-LABEL: @not_dominate(
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entry:
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%a1 = add i32 %a, 1
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br i1 %cond, label %then, label %merge
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then:
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%mul0 = mul i32 %a, %b
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; CHECK: %mul0 = mul i32 %a, %b
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%v0 = call i32 @foo(i32 %mul0)
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br label %merge
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merge:
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%v0.phi = phi i32 [ 0, %entry ], [ %mul0, %then ]
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%mul1 = mul i32 %a1, %b
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; CHECK: %mul1 = mul i32 %a1, %b
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%v1 = call i32 @foo(i32 %mul1)
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%sum = add i32 %v0.phi, %v1
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ret i32 %sum
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}
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