[PPCISelLowering] avoid emitting libcalls to __mulodi4()

Similar to D108842, D108844, and D108926.

__has_builtin(builtin_mul_overflow) returns true for 32b PPC targets,
but Clang is deferring to compiler RT when encountering long long types.
This breaks ppc44x_defconfig + CONFIG_BLK_DEV_NBD=y builds of the Linux
kernel that are using builtin_mul_overflow with these types for these
targets.

If the semantics of __has_builtin mean "the compiler resolves these,
always" then we shouldn't conditionally emit a libcall.

This will still need to be worked around in the Linux kernel in order to
continue to support these builds of the Linux kernel for this
target with older releases of clang.

Link: https://bugs.llvm.org/show_bug.cgi?id=28629
Link: ClangBuiltLinux/linux#1438

Reviewed By: nemanjai

Differential Revision: https://reviews.llvm.org/D108936

Author: nickdesaulniers

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

@@ -1301,6 +1301,7 @@ PPCTargetLowering::PPCTargetLowering(const PPCTargetMachine &TM,
     setLibcallName(RTLIB::SHL_I128, nullptr);
     setLibcallName(RTLIB::SRL_I128, nullptr);
     setLibcallName(RTLIB::SRA_I128, nullptr);
+    setLibcallName(RTLIB::MULO_I64, nullptr);
   }
 
   if (!isPPC64)

llvm/test/CodeGen/PowerPC/overflow-intrinsic-optimizations.ll

@@ -0,0 +1,19 @@
+; RUN: llc %s -mtriple=powerpc -o - | FileCheck %s
+
+define i1 @no__mulodi4(i32 %a, i64 %b, i32* %c) {
+; CHECK-LABEL: no__mulodi4
+; CHECK-NOT: bl __mulodi4
+entry:
+  %0 = sext i32 %a to i64
+  %1 = call { i64, i1 } @llvm.smul.with.overflow.i64(i64 %0, i64 %b)
+  %2 = extractvalue { i64, i1 } %1, 1
+  %3 = extractvalue { i64, i1 } %1, 0
+  %4 = trunc i64 %3 to i32
+  %5 = sext i32 %4 to i64
+  %6 = icmp ne i64 %3, %5
+  %7 = or i1 %2, %6
+  store i32 %4, i32* %c, align 4
+  ret i1 %7
+}
+
+declare { i64, i1 } @llvm.smul.with.overflow.i64(i64, i64)