Implement a mechanism to disable GEP->PHI InstCombiner. #231
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andcarminati
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abhinay-anubola,
abnikant,
gbossu,
khallouh,
konstantinschwarz,
martien-de-jong,
SagarMaheshwari99 and
stephenneuendorffer
as code owners
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QoR results: This affects other benchmarks whose results are not visible. For example Add2D_bf16_1: aie-public: This PR: If we turn our eyes to the post-swp, we have: |
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| ; CHECK: bb3: | ||
| ; CHECK-NEXT: [[PHI:%.*]] = phi ptr [ [[TMP10]], [[BB1]] ], [ [[TMP4]], [[BB2]] ] | ||
| ; CHECK-NEXT: [[TMP25:%.*]] = load i32, ptr [[PHI]], align 4 | ||
| ; CHECK-NEXT: ret i32 [[TMP25]] |
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Ah. Probably the combine is better for very local alias analysis that doesn't want to follow too many PHI nodes
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In our case the PHI in bb3 dominates one of the GEPs?
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In our case, one GEP should reach the load. The combiner basically does the following for this case:
%struct = type { i32, i32 }
define i32 @dontFoldGEPs(ptr %dm, i1 %arg4, i64 %arg9, i64 %arg19) {
bb:
%0 = load ptr, ptr %dm, align 8
br i1 %arg4, label %bb1, label %bb2
bb1: ; preds = %bb
%1 = trunc i64 %arg9 to i20
br label %bb3
bb2: ; preds = %bb
%2 = trunc i64 %arg19 to i20
br label %bb3
bb3: ; preds = %bb2, %bb1
%.pn = phi i20 [ %1, %bb1 ], [ %2, %bb2 ]
%phi = getelementptr inbounds %struct, ptr %0, i20 %.pn
%3 = load i32, ptr %phi, align 4
ret i32 %3
}
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This helps to generate cleaner MIR for several kernels.