[MLIR][OpenMP][OMPIRBuilder] Add lowering support for omp.target_triples (#100156)

This patch modifies MLIR to LLVM IR lowering of the OpenMP dialect to take into
consideration the contents of the `omp.target_triples` module attribute while
generating code for `omp.target` operations.

It adds the `OpenMPIRBuilderConfig::TargetTriples` field and initializes it
using the `amendOperation` flow of the `OpenMPToLLVMIRTranslation` pass. Some
changes are introduced into the `OpenMPIRBuilder` to allow passing the
information about whether a target region is intended to be offloaded from
outside.

The result of this change is that offloading calls are only generated when the
`--offload-arch` or `-fopenmp-targets` options are given to the compiler.
Otherwise, only the host fallback code is generated. This fixes linker errors
currently triggered by `flang-new` if a source file containing a `target`
construct is compiled without any of the aforementioned options.

Several unit tests impacted by these changes, which are intended to check host
code generated for `omp.target` operations, are updated to contain the new
attribute. Without it, no calls to `__tgt_target_kernel` and associated control
flow operations are generated.

Fixes #100209.

1 files changed, 6 insertions, 4 deletions

diff --git a/llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp b/llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp
index cb4c289..6207792 100644
--- a/llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp
+++ b/llvm/unittests/Frontend/OpenMPIRBuilderTest.cpp
@@ -5983,8 +5983,8 @@ TEST_F(OpenMPIRBuilderTest, TargetRegion) {
   TargetRegionEntryInfo EntryInfo("func", 42, 4711, 17);
   OpenMPIRBuilder::LocationDescription OmpLoc({Builder.saveIP(), DL});
   Builder.restoreIP(OMPBuilder.createTarget(
-      OmpLoc, Builder.saveIP(), Builder.saveIP(), EntryInfo, -1, 0, Inputs,
-      GenMapInfoCB, BodyGenCB, SimpleArgAccessorCB));
+      OmpLoc, /*IsOffloadEntry=*/true, Builder.saveIP(), Builder.saveIP(),
+      EntryInfo, -1, 0, Inputs, GenMapInfoCB, BodyGenCB, SimpleArgAccessorCB));
   OMPBuilder.finalize();
   Builder.CreateRetVoid();
 
@@ -6087,7 +6087,8 @@ TEST_F(OpenMPIRBuilderTest, TargetRegionDevice) {
                                   /*Line=*/3, /*Count=*/0);
 
   Builder.restoreIP(
-      OMPBuilder.createTarget(Loc, EntryIP, EntryIP, EntryInfo, /*NumTeams=*/-1,
+      OMPBuilder.createTarget(Loc, /*IsOffloadEntry=*/true, EntryIP, EntryIP,
+                              EntryInfo, /*NumTeams=*/-1,
                               /*NumThreads=*/0, CapturedArgs, GenMapInfoCB,
                               BodyGenCB, SimpleArgAccessorCB));
 
@@ -6235,7 +6236,8 @@ TEST_F(OpenMPIRBuilderTest, ConstantAllocaRaise) {
                                   /*Line=*/3, /*Count=*/0);
 
   Builder.restoreIP(
-      OMPBuilder.createTarget(Loc, EntryIP, EntryIP, EntryInfo, /*NumTeams=*/-1,
+      OMPBuilder.createTarget(Loc, /*IsOffloadEntry=*/true, EntryIP, EntryIP,
+                              EntryInfo, /*NumTeams=*/-1,
                               /*NumThreads=*/0, CapturedArgs, GenMapInfoCB,
                               BodyGenCB, SimpleArgAccessorCB));