Index: llvm/trunk/docs/LangRef.rst =================================================================== --- llvm/trunk/docs/LangRef.rst +++ llvm/trunk/docs/LangRef.rst @@ -5381,7 +5381,7 @@ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ This metadata disables all optional loop transformations unless -explicitly instructed using other transformation metdata such as +explicitly instructed using other transformation metadata such as ``llvm.loop.unroll.enable``. That is, no heuristic will try to determine whether a transformation is profitable. The purpose is to avoid that the loop is transformed to a different loop before an explicitly requested @@ -5720,10 +5720,24 @@ '``llvm.loop.distribute.followup_all``' Metadata ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -Thes attributes in this metdata is added to all followup loops of the +The attributes in this metadata is added to all followup loops of the loop distribution pass. See :ref:`Transformation Metadata ` for details. +'``llvm.licm.disable``' Metadata +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +This metadata indicates that loop-invariant code motion (LICM) should not be +performed on this loop. The metadata has a single operand which is the string +``llvm.licm.disable``. For example: + +.. code-block:: llvm + + !0 = !{!"llvm.licm.disable"} + +Note that although it operates per loop it isn't given the llvm.loop prefix +as it is not affected by the ``llvm.loop.disable_nonforced`` metadata. + '``llvm.access.group``' Metadata ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Index: llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h =================================================================== --- llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h +++ llvm/trunk/include/llvm/Transforms/Utils/LoopUtils.h @@ -215,6 +215,9 @@ /// Look for the loop attribute that disables all transformation heuristic. bool hasDisableAllTransformsHint(const Loop *L); +/// Look for the loop attribute that disables the LICM transformation heuristics. +bool hasDisableLICMTransformsHint(const Loop *L); + /// The mode sets how eager a transformation should be applied. enum TransformationMode { /// The pass can use heuristics to determine whether a transformation should Index: llvm/trunk/lib/Transforms/Scalar/LICM.cpp =================================================================== --- llvm/trunk/lib/Transforms/Scalar/LICM.cpp +++ llvm/trunk/lib/Transforms/Scalar/LICM.cpp @@ -330,6 +330,12 @@ assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form."); + // If this loop has metadata indicating that LICM is not to be performed then + // just exit. + if (hasDisableLICMTransformsHint(L)) { + return false; + } + std::unique_ptr CurAST; std::unique_ptr MSSAU; bool NoOfMemAccTooLarge = false; Index: llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp =================================================================== --- llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp +++ llvm/trunk/lib/Transforms/Utils/LoopUtils.cpp @@ -45,6 +45,7 @@ #define DEBUG_TYPE "loop-utils" static const char *LLVMLoopDisableNonforced = "llvm.loop.disable_nonforced"; +static const char *LLVMLoopDisableLICM = "llvm.licm.disable"; bool llvm::formDedicatedExitBlocks(Loop *L, DominatorTree *DT, LoopInfo *LI, MemorySSAUpdater *MSSAU, @@ -379,6 +380,10 @@ return getBooleanLoopAttribute(L, LLVMLoopDisableNonforced); } +bool llvm::hasDisableLICMTransformsHint(const Loop *L) { + return getBooleanLoopAttribute(L, LLVMLoopDisableLICM); +} + TransformationMode llvm::hasUnrollTransformation(Loop *L) { if (getBooleanLoopAttribute(L, "llvm.loop.unroll.disable")) return TM_SuppressedByUser; Index: llvm/trunk/test/Transforms/LICM/pragma-licm-disable.ll =================================================================== --- llvm/trunk/test/Transforms/LICM/pragma-licm-disable.ll +++ llvm/trunk/test/Transforms/LICM/pragma-licm-disable.ll @@ -0,0 +1,33 @@ +; RUN: opt < %s -S -basicaa -licm | FileCheck %s + +; Check that the LICM pass does not operate on a loop which has the +; llvm.licm.disable metadata. +; CHECK-LABEL: @licm_disable +; CHECK: entry: +; CHECK-NOT: load +; CHECK: do.body: +; CHECK: load i64, i64* bitcast (i32** @in to i64*) + +target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128" +target triple = "x86_64-pc-windows-msvc" + +@in = internal unnamed_addr global i32* null, align 8 +@out = internal unnamed_addr global i32* null, align 8 + +define void @licm_disable(i32 %N) { +entry: + br label %do.body + +do.body: ; preds = %entry + %i.0 = phi i32 [ 0, %entry ], [ %inc, %do.body ] + %v1 = load i64, i64* bitcast (i32** @in to i64*), align 8 + store i64 %v1, i64* bitcast (i32** @out to i64*), align 8 + %inc = add nsw i32 %i.0, 1 + %cmp = icmp slt i32 %inc, %N + br i1 %cmp, label %do.body, label %do.end, !llvm.loop !1 + +do.end: ; preds = %do.body + ret void +} +!1 = !{!1, !2} +!2 = !{!"llvm.licm.disable"}