Index: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
@@ -304,7 +304,17 @@
   setOperationAction(ISD::SIGN_EXTEND_INREG, MVT::i8   , Legal);
   setOperationAction(ISD::SIGN_EXTEND_INREG, MVT::i1   , Expand);
   setOperationAction(ISD::FP_ROUND_INREG   , MVT::f32  , Expand);
-  setOperationAction(ISD::FREM             , MVT::f32  , Expand);
+
+  if (Subtarget->is32Bit() && Subtarget->isTargetKnownWindowsMSVC()) {
+    // On 32 bit MSVC, `fmodf(f32)` is not defined - only `fmod(f64)`
+    // is. We should promote the value to 64-bits to solve this.
+    // This is what the CRT headers do - `fmodf` is an inline header
+    // function casting to f64 and calling `fmod`.
+    setOperationAction(ISD::FREM           , MVT::f32  , Promote);
+  } else {
+    setOperationAction(ISD::FREM           , MVT::f32  , Expand);
+  }
+
   setOperationAction(ISD::FREM             , MVT::f64  , Expand);
   setOperationAction(ISD::FREM             , MVT::f80  , Expand);
   setOperationAction(ISD::FLT_ROUNDS_      , MVT::i32  , Custom);
Index: llvm/trunk/test/CodeGen/X86/frem-msvc32.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/frem-msvc32.ll
+++ llvm/trunk/test/CodeGen/X86/frem-msvc32.ll
@@ -0,0 +1,12 @@
+; Make sure that 32-bit FREM is promoted to 64-bit FREM on 32-bit MSVC.
+
+; MSVC does not have a 32-bit fmodf function, so it must be promoted to
+; a 64-bit fmod rtlib call.
+; RUN: llc -mtriple=i686-pc-windows-msvc -O0 < %s  | FileCheck %s
+
+; CHECK: @do_frem32
+; CHECK: {{_fmod$}}
+define float @do_frem32(float %a, float %b) {
+    %val = frem float %a, %b
+    ret float %val
+}