diff --git a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp --- a/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp +++ b/llvm/lib/Transforms/Vectorize/LoopVectorize.cpp @@ -9441,6 +9441,51 @@ return true; } +// Emit a remark if there are stores to floats that required a floating point +// extension. If the vectorized loop was generated with floating point there +// will be a performance penalty from the conversion overhead and the change in +// the vector width. +static void checkMixedPrecision(Loop *L, OptimizationRemarkEmitter *ORE) { + SmallVector Worklist; + for (BasicBlock *BB : L->getBlocks()) { + for (Instruction &Inst : *BB) { + if (auto *S = dyn_cast(&Inst)) { + if (S->getValueOperand()->getType()->isFloatTy()) + Worklist.push_back(S); + } + } + } + + // Traverse the floating point stores upwards searching, for floating point + // conversions. + SmallPtrSet Visited; + SmallPtrSet EmittedRemark; + while (!Worklist.empty()) { + auto *I = Worklist.pop_back_val(); + if (!L->contains(I)) + continue; + if (!Visited.insert(I).second) + continue; + + // Emit a remark if the floating point store required a floating + // point conversion. + // TODO: More work could be done to identify the root cause such as a + // constant or a function return type and point the user to it. + if (isa(I) && EmittedRemark.insert(I).second) + ORE->emit([&]() { + return OptimizationRemarkAnalysis(LV_NAME, "VectorMixedPrecision", + I->getDebugLoc(), L->getHeader()) + << "floating point conversion changes vector width. " + << "Mixed floating point precision requires an up/down " + << "cast that will negatively impact performance."; + }); + + for (Use &Op : I->operands()) + if (auto *OpI = dyn_cast(Op)) + Worklist.push_back(OpI); + } +} + LoopVectorizePass::LoopVectorizePass(LoopVectorizeOptions Opts) : InterleaveOnlyWhenForced(Opts.InterleaveOnlyWhenForced || !EnableLoopInterleaving), @@ -9759,6 +9804,9 @@ << NV("VectorizationFactor", VF.Width) << ", interleaved count: " << NV("InterleaveCount", IC) << ")"; }); + + if (ORE->allowExtraAnalysis(LV_NAME)) + checkMixedPrecision(L, ORE); } Optional RemainderLoopID = diff --git a/llvm/test/Transforms/LoopVectorize/mixed-precision-remarks.ll b/llvm/test/Transforms/LoopVectorize/mixed-precision-remarks.ll new file mode 100644 --- /dev/null +++ b/llvm/test/Transforms/LoopVectorize/mixed-precision-remarks.ll @@ -0,0 +1,69 @@ +; RUN: opt -force-vector-interleave=2 -force-vector-width=4 -loop-vectorize -pass-remarks-analysis=loop-vectorize -disable-output < %s 2>&1 | FileCheck %s + +; CHECK: remark: mixed-precision.c:3:26: floating point conversion changes vector width. Mixed floating point precision requires an up/down cast that will negatively impact performance. +define void @f(float* noalias nocapture %X, i64 %N) { +entry: + br label %for.body + +for.cond.cleanup: + ret void + +for.body: + %i = phi i64 [ %inc, %for.body ], [ 0, %entry ] + %arrayidx = getelementptr inbounds float, float* %X, i64 %i + %0 = load float, float* %arrayidx, align 4 + %conv = fpext float %0 to double, !dbg !9 + %mul = fmul double %conv, 0x3FD5555555555555 + %conv3 = fptrunc double %mul to float + store float %conv3, float* %arrayidx, align 4 + %inc = add nuw i64 %i, 1 + %exitcond.not = icmp eq i64 %inc, %N + br i1 %exitcond.not, label %for.cond.cleanup, label %for.body +} + +; CHECK: remark: mixed-precision.c:8:8: floating point conversion changes vector width. Mixed floating point precision requires an up/down cast that will negatively impact performance. +; CHECK: remark: mixed-precision.c:7:16: floating point conversion changes vector width. Mixed floating point precision requires an up/down cast that will negatively impact performance. +; CHECK-NOT: remark: mixed-precision.c:7:16: floating point conversion changes vector width. Mixed floating point precision requires an up/down cast that will negatively impact performance. +define void @g(float* noalias nocapture %X, float* noalias nocapture %Y, i64 %N) { +entry: + %pi = alloca double + store double 0x400921FB54442D18, double* %pi + %fac = load double, double* %pi + br label %for.body + +for.body: + %i = phi i64 [ %inc, %for.body ], [ 0, %entry ] + %arrayidx = getelementptr inbounds float, float* %X, i64 %i + %0 = load float, float* %arrayidx, align 4 + %conv = fpext float %0 to double, !dbg !10 + %mul = fmul double %conv, %fac + %conv1 = fptrunc double %mul to float + store float %conv1, float* %arrayidx, align 4 + %arrayidx5 = getelementptr inbounds float, float* %Y, i64 %i + %1 = load float, float* %arrayidx5, align 4 + %conv2 = fpext float %1 to double, !dbg !11 + %mul2 = fmul double %conv2, %fac + %conv3 = fptrunc double %mul2 to float + store float %conv3, float* %arrayidx5, align 4 + %inc = add nuw nsw i64 %i, 1 + %exitcond.not = icmp eq i64 %inc, %N + br i1 %exitcond.not, label %for.cond.cleanup, label %for.body + +for.cond.cleanup: + ret void +} + +!llvm.dbg.cu = !{!0} +!llvm.module.flags = !{!3, !4} + +!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 12.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: NoDebug, enums: !2, splitDebugInlining: false, nameTableKind: None) +!1 = !DIFile(filename: "mixed-precision.c", directory: "/tmp/mixed-precision.c") +!2 = !{} +!3 = !{i32 2, !"Debug Info Version", i32 3} +!4 = !{i32 1, !"wchar_size", i32 4} +!6 = distinct !DISubprogram(name: "f", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2) +!7 = distinct !DISubprogram(name: "g", scope: !1, file: !1, line: 5, type: !8, scopeLine: 5, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !2) +!8 = !DISubroutineType(types: !2) +!9 = !DILocation(line: 3, column: 26, scope: !6) +!10 = !DILocation(line: 7, column: 16, scope: !7) +!11 = !DILocation(line: 8, column: 8, scope: !7)